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Undertale Yellow - TV Tropes

  • ️Thu Dec 15 2016

WARNING: This fangame is made with the assumption that players have already experienced Undertale, so spoilers relating to backstory in that game will be unmarked.

Undertale Yellow (Video Game)

* Five humans, missing...

Before the seventh, there was another.

Undertale Yellow is a fan prequel to Undertale, created and led by Master Sword with the help of several developers under the collective name Team Undertale Yellow (or Team UTY for short). Set some time after the human-monster war, the story focuses on Clover, a human child and the source of the original game's Yellow SOUL. When several humans mysteriously start going missing while travelling to Mt. Ebott, Clover decides to jump into the Underground themself to look for them. Their adventure has both new and familiar faces.

Announced only a few months after the release of the original game, the project started on February 4, 2016 after Toby Fox allowed it to be greenlit. A demo was made available on Gamejolt in March of the same year, with the game finally releasing on December 9, 2023, available to download here on Gamejolt.

Undertale Yellow provides examples of:

  • 11th-Hour Superpower:
    • During the Final Boss of each route, Clover's SOUL gains the shooting ability of the yellow SOUL from Undertale, giving Clover a means of attacking during the enemy's turn.
    • In the Genocide run specifically, Martlet artificially gains one. Before the final fight on the roof, she injects herself with Determination, that she stole from Alphys' lab to give herself a boost. Although, players of Undertale would be able to guess Martlet's grim fate (and, indeed, that of any monster that takes Determination), but in a surprising twist of events, she dies not because of the Determination being too much for her, but rather because her body accumulates too much damage to maintain her form, heavily implying she's seemingly the only monster that can utilize Determination without dying.
  • Absurdly High Level Cap: Just as in Undertale, the maximum LOVE is 20, which is only obtained after defeating the Final Boss of the Genocide route, at which point you'll have killed every monster. There's one more encounter after that, but it's a Post-Final Boss fight who gets taken out in a cutscene.
  • Abandoned Laboratory: The Steamworks is an entire area adjacent to Hotland in an extreme state of decay. There are no monsters whatsoever except a former scientist hiding in the walls, power is down until you restore it, most of the robots are malfunctioning, and whatever parts of the facility haven't melted yet, they are overtaken by the very plants they were studying.
  • Abnormal Ammo: Instead of changing weapons, Clover keeps their gun and changes the ammo. The various kinds of ammo they can use include pebbles, ice, coffee beans, glass shards, and nails. Depending on the ammo equipped, Clover can receive different buffs for landing a critical hit such as increased speed for a turn when using the coffee ammo.
  • Accidental Murder: You do this to Pops in the Genocide run. You don't know the balloon is alive until after you get a "funny" voice, causing Mood Whiplash.
  • Action Commands: When attacking, an eye-like meter will appear over the menu, and a bullseye-like circle will run across it. Confirm the attack when the bar is near the middle, and you do more damage. Don't press anything, and you won't attack.
  • Adaptational Villainy: In Undertale, the only description for the Old Tutu and Ballet Shoes in Waterfall was that the former is covered in dust and the latter made Frisk feel "incredibly dangerous" when putting them on, leaving it ambiguous whether Integrity killed monsters maliciously or out of self-preservation. Outside of that, they help Frisk out during the Neutral and Pacifist routes like the other souls. In Undertale Yellow, they come across as distinctively more morally dubious. They almost killed Kanako and Dalv in retaliation for being attacked by the latter, the former being a young child, is overall described as violent by the other characters and sources, had killed several monsters during their attack in Snowdin, and is ultimately killed by Axis in Waterfall when they attempted to flee from the monsters (albeit unintentionally).
  • Air-Vent Passageway: In the Neutral and Pacifist routes, you escape from the rooms Axis sends you to by going through the vents.
  • Alien Kudzu: The bizarre white plants you see with increasing frequency in Steamworks. Other than them being white, they grow on any kind of surface, leave behind black sludge once rotted, can produce electricity, and grow four times faster than normal plants. The lab they came from is completely swallowed by them, and they even grew on the robots. They're described as smelling unnatural, and Ceroba discusses the possibility they're harmful to humans through inhalation.
  • All for Nothing:
    • In the flawed pacifist ending, Martlet's idealism is smashed to pieces when all of her efforts to keep Clover safe and find a happy ending are dashed when Asgore kills Clover.
    • In the true pacifist ending, Flowey gives up on getting what they want from Clover, allowing their hundreds of attempts and resets to go to waste as the flower lets the timeline continue, waiting for the next human in the hopes they'll do better.
  • Always Accurate Attack: Just like in Undertale battles, the player's attacks always hit unless they deliberately miss.
  • Ambiguous Ending: While it's presumed that one of the two Pacifist endings is the "canon" one, it's left unclear which is the true canon one, as elements of both can apply to the original game:
    • At first glance, it can be presumed that the ending from killing the pacifist run's Final Boss is the canon one. It leads Clover to their death at Asgore's hands, and supplementary information can be interpreted as Asgore had personally killed every child before Frisk. However, a secret recording indicates that Axis had previously killed the child with the blue SOUL.
    • In contrast, the ending where the Pacifist route's Final Boss is spared has Clover giving up their SOUL for the benefit of monsterkind. While this clashes with the previous Asgore theory, it's only this ending that shows Clover's belongings being deposited into the Waterfall trash disposal, which is where Bratty and Catty found them in the original game. In addition, it's only this ending that directly leads into the original game, as the final screen is Clover's SOUL hearing Frisk's call for help.
  • Ambiguously Evil: Flowey. He's seemingly helpful, even saving your progress. However, the game doesn't make his true intentions clear until the endings; while the Neutral and Genocide routes confirm that he's very much the same manipulative jerk he was in Undertale, both of the Pacifist endings has him keep up his friendly facade and leave Clover alone after they are either killed by Asgore or sacrifice their SOUL for the underground.
  • Ambiguous Gender: According to Word of God, Clover's gender is canonically up to player interpretation, and Clover is only ever referred to with they/them pronouns.
  • And I Must Scream: The entire Neutral Route Flowey battle, which takes place after he kills Clover and absorbs their SOUL, with them trapped in his mind and trying to avoid being completely absorbed.
  • Anti-Climax: The Neutral route ends this way. After a long-fought battle against Flowey in the nightmarish hellscape of his mind, he eventually just… stops, realizing that the whole battle between him and Clover is pointless, and urges Clover to try a different path before resetting the timeline.
  • Anti-Frustration Features:
    • Getting any particular ending you want is easier and doesn't affect subsequent playthroughs. Unlike Undertale, you can do the Pacifist route from the get-go; you don't have to do a Neutral route first. Also, doing a Genocide route doesn't taint future Neutral and/or Pacifist runs.
    • There are a few accessibility options in the menu, such as Auto-Run and being able to restart battles when you die instead of reloading your last save.
    • You can turn on a few features to make boss battles easier if you're unable to keep up. The final bosses of all three routes present the player with the option to turn on auto-fire, in case needing to shoot and dodge at the same time is too much. Also, the battle with El Bailador has a Rhythm Game-esque dance, and you can turn on Auto-Rhythm to automatically hit the notes as long as the SOUL is in the right spot.
    • Partway through the game, you gain access to the Dimensional Satchel. This lets you exchange items between your inventory and storage, saving you the need to backtrack.
    • During the part where Axis chases you in the Steamworks, he slows down a bit every time you get caught.
    • When doing a Genocide run, if you try to trigger an encounter in a room where all the enemies are dead, an "X" shows up in a speech bubble to let you know that you can move on.
    • Using an attack on an enemy that would leave it with extremely low HP will cause the attack to be "rounded" up and kill the enemy instead.
    • An easy mode option was patched in post-release after the base game proved to be too difficult for some players, which gives Clover's hat 3 defense points.
  • Animation Bump: The game's sprite work is much more fluid and detailed than Undertale. Additionally, climax fights will have much more animation than other fights to increase the drama.
  • Art Shift: The final battle in the Neutral Route has a bunch of these with Flowey's different forms. These are a 2D-animated depiction of him as a beating heart, a papercraft version of himself, another 2D-animated version of himself that vaguely resembles a rubberhose artstyle, an N64-style ragdoll version of himself with some 2D elements that most closely resembles the Yoshi's Story artstyle, a vaguely Stop Motion version of himself that resembles the artstyle of 3D SNES games such as Donkey Kong Country, and another N64-esque version of himself that's reminiscent of The Legend of Zelda: Majora's Mask. To say nothing of the painterly style that his default self is in, as well as the 2D-animated attacks.
  • Artificial Sun: At some point in the past the mines uncovered an absolutely gigantic round Heatstone. You can see it from the Summit and it literally looks like the sun embedded in a mountain peak. Several monsters comment how its unearthing completely destroyed the local ecosystem, turning the area from the Meadow to the Dunes. Some monsters are still trying to preserve the original plants but it's not going very well. At least the mines and the Dunes look bright, unlike every other area in the Underground.
  • Ascended Extra: In the main game, the owner of the yellow SOUL was just one of the six humans who fell into the Underground and died, with their backstory only vaguely hinted at through their virtue and the equipment they left behind. Here, they're given a name with "Clover" and shown to have an entire character arc.
  • Ascended Meme: During the Final Boss of a Neutral route, Recurring Fanon Character "Prunsel" briefly appears, and the vision during the same battle where Martlet melts in a facsimile of Snowdin to reveal an eye could also be a reference to it.
  • Background Music Override:
    • In a Pacifist or Neutral route, the Wild East has different variations of an upbeat tune, as well as two additional tracks that play in the saloon and Blackjack's shop. However, after the rest of the Feisty Five call Starlo out, the music is replaced with a more somber piece that plays everywhere in the town. This also occurs if Starlo is killed.
    • In the Pacifist route, both times when you are accompanied by Martlet after Steamworks have the usual music replaced with a more serious track — "The Trek" for when you have to go to Ceroba's house, and "Flock Together" for after you've met Martlet on the apartment roof and have decided to go to New Home together.
  • Bait-and-Switch: When you meet Flowey, it's similar to your first meeting Flowey in Undertale, but instead he helps you save and progress.
  • Big Bad: Flowey. It's to an even greater extent than in the original game — due to having the ability to SAVE, Flowey has complete control over Clover's adventure and is responsible for the route Clover was forced on.
  • Bitch in Sheep's Clothing: Near the end of a neutral route, Flowey betrays Clover and reveals that he's been resetting Clover's progress for a long time, only to be exasperated when they kept getting themself killed in the rest of the Underground. As a last resort, Flowey tampered with the switch in the Ruins to force them to take a different path, leading to the events in the game. He was only pretending to be their friend in the hope that they would be able to help him get the five SOULs from Asgore.
  • Bittersweet Ending: It's a given as a fan prequel, for Clover is one of the captured SOULs in Undertale, meaning they will die.
    • True Pacifist Ending: Clover refuses to kill Ceroba, who apologizes for everything she did, and is forgiven by Clover, Starlo, and Martlet. But Clover sacrifices their SOUL in order to help the monsters break the barrier and dies.
    • Flawed Pacifist Ending: Clover grants Ceroba's wish and Mercy Kills her. Starlo calls Clover "lower than dirt" and laments that he should've killed Clover, then leaves. Martlet takes Clover to see Asgore to try to talk things out, but they intend on fighting each other despite her pleas, so she leaves heartbroken. A Hopeless Boss Fight ensues, and Asgore kills Clover, taking their SOUL.
  • Blamed for Being Railroaded:
    • In the Genocide run, there is nothing you can do to stop Starlo from dying. Even if you wait, Starlo will shoot you with a harmless rubber bullet and Clover will shoot him automatically. Enraged, Ceroba charges at you to engage in a fight. Contrast this to other areas before and after the Ceroba fight where you can abort the Genocide run by either not exhausting the area of regular monsters or deciding not to kill the boss monster in question.
    • In the Neutral route, Flowey will be extremely pissed at Clover for deciding to talk to Martlet as opposed to going straight to Asgore, even though all paths to Asgore are blocked.
  • Bloodless Carnage: Like in Undertale, monsters turn to dust when killed, so no blood is spilled.
  • Bottomless Magazines: Even though you can change the type of ammunition you use, you never actually run out of bullets. That said, the number of shots you can fire depends on what kind of gun you have (with the revolver you can fire up to six per turn), so there's a chance Cover is reloading between turns. That doesn't make the ammo run out though.
  • Bread, Eggs, Milk, Squick: In the Neutral Route, if Clover asks Vendy about their creator after obtaining a Steamworks ID, Vendy rattles off thirty-one occupations Dr. Oscar has held. The twenty-seventh is "war criminal".
  • Brick Joke:
    • When Clover first approaches the Mines, they'll encounter a burly red miner running in the opposite direction, claiming to have been called to Snowdin for something. If they failed to free Slurpy (the monster from Snowdin trapped in a Tongue on the Flagpole), the Pacifist Route credits will show the miner unsuccessfully attempting to free Slurpy from the pole.
    • When Clover enters the Oasis, they can pay the fortune teller a tiny fee and she'll tell them they'll encounter a tumbleweed in their future. Cue the boss fight with Starlo, where a tumbleweed comes by and waves at Clover.
  • Bullet Hell: Enemies attack with bullets of varying shapes and patterns. Battles can become hectic, due to the more challenging nature of this game in comparison to vanilla Undertale.
  • Call-Forward:
    • One of the lines of Flavor Text in Axis' fight is "Death by metal & magic." This is a twofold reference to Mettaton, referencing Mettaton EX's theme, "Death by Glamour", and the answer to what robots are made out of according to Mettaton's quiz show, being "Metal & Magic".
    • One of the flavor text narrations for the Axis fight on a Genocide run is "In your way."
    • In the Neutral Final Boss, Flowey reveals at the end that everything is in his head and that once his plan reaches fruition, he'll manage to finally gain a physical form that will allow him to achieve what he always wanted, and that Clover will be there to watch. This is referencing the final battle of Undertale's Neutral Route.
    • Going to the alley left of the UG Apartments will lead you to a wall that you can check. The description reads "An ordinary wall?". Note the question mark. This references how Sans uses this path as a "shortcut" to get you in the MTT Resort.
  • Chain of Deals: There's a quest in Snowdin where you have to bring some coffee to a monster who got their tongue stuck to a lamp post, but the coffee you buy from the Honeydew Resort is too hot, so you have to give it to a different NPC, who gives you an item to give to another, and so on until you get an item to give to the first NPC who will then give you back the coffee that has now cooled down. Bringing the cooler coffee back to the stuck NPC will complete the quest and reward you with a defense item that heals 2 HP every turn.
  • Comically Missing the Point: Investigate one of the drawers in Chujin's office, and you'll find the records he kept of every monster he befriended. Martlet reads the names aloud, but when she gets to her own name, she is shocked that Chujin found another monster with her name and says that she can't believe it never came up in conversation.
  • Controllable Helplessness: At the end of the Neutral route, the entire fight with Flowey is after he's killed Clover and taken their SOUL into himself. The whole nightmare sequence is Clover's SOUL resisting being fully absorbed, and while Flowey does eventually give up (if only because he doesn't want to become Sealed Evil in a Duel), it doesn't change the fact that Clover is already dead and their SOUL has nowhere to return to.
  • Continuity Nod:
    • Numerous characters from Undertale such as Undyne, Alphys, and Mettaton are mentioned directly or indirectly, even if not shown in person.
    • There's a list of award-winning Underground scientists in the Steamworks, among which is Chujin, but one accolade appears to be entirely obscured, with only a line about being awarded for C (word gets cut off), recalling the numerous hidden references to Gaster in both Undertale and Deltarune. The reference to a "top scientist" working on an alternative to the white plants as a source of power for the Underground could also reference him.
    • There's a list on a bulletin board in the UG Apartments (future MTT resort) that mentions a "magma smoothie" contest. Among the participants were Pyrope, Grillby, Fuku Fire, and Heats Flamesman. None of those monsters appear in this game. And no, they don't remember Heats Flamesman's name here either.
  • Cosmetically-Advanced Prequel: Downplayed, but it's there. In particular, battles are notably more colorful and dynamic, as well as having a more varied soundtrack. There's also more animation on the boss fights, and all bosses and minibosses get custom backgrounds.
  • Cruel Mercy: Dalv is the only boss you can spare without aborting a Genocide run, and he'll even call you out on leaving him the only one alive. He wanted to be alone, and now he's got it.
  • Crossover Cameo: In the Dunes, Red from another fangame, Undertale Red, can be met, having apparently been wrongly arrested by Martlet prior to the events of the story. Though she's willing to bury the hatchet once things are explained. Later, in the Wild East, Cooper, a character from Undertale Green, can be interacted with, where he talks about his dislike for puzzles.
  • Curb-Stomp Battle: This is how the Asgore "fight" plays out at the end of a Genocide run, just like in Undertale proper.
  • Cycle of Revenge: When Clover confronts Asgore in the Genocide ending, he tells them that their actions have ensured the war between humans and monsters will never end, and that many people on both sides will die as a result. Humanity attacked the monsters, Asgore gave into revenge when his children died, and now Clover has done the same by murdering countless monsters. It's implied on the True Pacifist Route that Clover realizes this and decides to sacrifice themselves to try and set it right.
  • Darker and Edgier: With a Doomed Protagonist, the game has an unintentionally depressing atmosphere.
    • This extends to the Pacifist route; in the original game, aside from the Amalgamates, which are eventually shown to be friendly, the Pacifist route is a mostly charming, heartwarming story that serves as a palate cleanser after the horror-laden ending of the Neutral route, with the final battle against a revived but redeemable Asriel Dreemur. In this game, the Pacifist route ends with Clover's alleged close companion, Ceroba, revealing that she plans to kill them and use their SOUL, leading to an emotional battle as her tragic backstory is laid bare and she begs for Clover to die so that she can complete her work. The player even has the choice of killing her but still continuing on a Pacifist route. Even if Ceroba is spared, Clover will still end up dying, albeit on their own terms.
      • This even extends to both routes' usage of the "Hopes and Dreams" leitmotif; in the original game, it's used as a triumphant indicator of an impossible-to-lose final battle, whereas in this game, it's used to signify Ceroba's Rage Breaking Point.
    • The Neutral Route's ending is somehow even more surreal and horrific than the original game's, giving us such lovely sights as Martlet being killed by Flowey and blaming Clover in her final moments, Flowey later bringing up an apparition of her face melting away, and the entire psychological horror-laden final battle.
  • Dead Hat Shot: The True Pacifist Ending screen shows Clover's hat and gun on the bed of flowers in Waterfall.
  • Deconstructed Trope: As per being an Undertale fan game, Level Grinding gets the same results as it did in Undertale, with multiple monsters treating you like a murderous psychopath for going out of your way to kill every monster in the area. Even Flowey will start calling you out on this after a while. That said, unlike Undertale where it's treated as downright deplorable, Yellow takes a slightly different approach. The Genocide Route is the only route where Clover can pull a Screw Destiny and make it out of the underground alive and take the other human SOULs with them. However, this still means having to murder everyone Clover comes across, and multiple monsters call Clover out that while the royal guard may have killed five human children before them for the sake of leaving the underground, Clover is actively going out of their way to punish monsters who are in no way related to those who actually did the deed. This makes the theme of the Genocide Route a Driving Question: do those who are part of a group that has committed a horrible act deserve to be punished, even if they didn't commit the act in question?
  • Deliberate Values Dissonance: Dina says most monsters think it's weird to own pets. She has a few pet snakes herself.
  • Developer's Foresight:
    • The Steamworks vending robot acts rude to Clover because they're an unauthorized trespasser. Sure enough, if you come back after making yourself a Steamworks ID in the Neutral route, Vendy's dialogue will completely change to be more hospitable since Clover is now recognized as an employee.
    • You usually have to kill at least one monster in order to get into the Neutral route and subsequent ending. However, it’s possible to lock yourself out of the Pacifist route even if you didn’t gain any EXP, like if you decide to only fight the robots in Steamworks sans Axis when Ceroba is with you. In this more obscure variation, Martlet is noticeably less hesitant and wary of Clover during the conversation at the rooftop and her reaction to being killed by Flowey is one of misplaced disbelief rather than misplaced betrayal.
    • In the Neutral final fight, the replicated boss attacks will only correspond to which of the game's bosses you defeated through violence. Any that didn't go down in a violent fashion have their attacks skipped. Notably, Ceroba's attack is only available on a genocide run that was aborted past the Wild East, since the fight is exclusive to that route.
    • Like in Undertale, Flowey will give new dialogue after his fight if you do multiple Neutral Routes.
    • Also like in Undertale, there's unique dialogue you can get for going further and further without saving the game even once. In particular, Flowey gets more and more frustrated with you for not saving, which even includes getting to the Final Boss of a Neutral route.
    • An odd aversion that's showcased in this video. If you have 0G before interacting with the wishing well with Martlet, the cutscene in which you lend Martlet 1G to make a wish still plays out despite you not having any money to give her.
  • Disc-One Nuke: By doing the Chain of Deals to free the kid stuck to the pole in Snowdin, Clover acquires a Silver Scarf, a 6 DEF item that heals them for 2 HP every turn. If the player is doing a Neutral playthrough, this item effectively makes the rest of the game a breeze aside from the route's Final Boss, as the DEF and extra HP acquired from LV more than makes up for the missing DEF from later accessories in favor of free healing.
  • Doomed by Canon: Given the situation at the start of Undertale, it is not likely that Clover will live after the adventure. Indeed, Flowey RESETS at the end of the Neutral Route and brings Clover back to the beginning of the game, keeping them trapped in a time loop until they get another ending. At the end of the Pacifist Route, by killing Ceroba, Martlet takes Clover to Asgore, who ultimately kills them in battle, or in the True Pacifist Ending, after sparing Ceroba, Clover willingly gives up their SOUL so the monsters can break the barrier someday. Regardless of the result, Flowey ultimately chooses not to RESET again to bring them back. Subverted in the Genocide route, where they become so powerful that they override Flowey's ability to SAVE, kill Asgore to absorb his SOUL, and ironically fulfill their original mission in a way by stealing the SOULs of the previous five humans and crossing the barrier with them. And if the player chooses, they can allow Clover to keep this ending.
  • Dramatic Irony: Ceroba senses that her daughter is still alive even after being sent to Alphys due to her state… With the location being the Lab, where at this point Kanako is most likely part of an Amalgamate.
  • Dull Eyes of Unhappiness: You know the Genocide run is in effect if Clover's eyes are obscured.
  • Earn Your Happy Ending: In a twisted kind of way, the Genocide ending is this for Clover, since they not only accomplish what they came down to do, but they also make it out alive with the SOULs.
  • Easter Egg: As with the original Undertale, this game also has FUN values that may prompt specific rare events, such as graffiti on the walls changing shape and/or location.
  • Entertainingly Wrong: North Star thinks horses are a type of monster and that it's physically possible to run to the sun. So this means that horses and humans are fireproof because they don't burn when they get there! There's no way to correct him on this.
  • Every Man Has His Price: Blackjack "hates" doing business with the Fiesty Five because of all the trouble they cause, but since the group can't tell how much his wares are actually worth he can rip them off. This is best shown when North Star tries to buy Clover a gun. At first Blackjack refuses, but then North Star says he'll pay 400G. Blackjack puts on his most pleasant customer service voice and accepts immediately. The gun in question normally costs half that money.
  • Eye Scream: When Clover kills Flowey at the end of the Genocide run, the first things that they shoot off are his eyes.
  • Fallen Hero: Clover is this regardless of previous playthroughs on a Genocide run, as unlike with Frisk, whose motivations for entering the Underground are ambiguous, Clover's motivations are undoubtedly good and their virtue is Justice.
  • Fantastic Light Source: The various glowing gemstones in the Dunes mine. Most notable is the gigantic swelterstone that looks like a sun, making the Dunes seem like they could be on the surface.
  • Five-Second Foreshadowing:
    • In the Steamworks greenhouse, blueprints for a robot model dubbed "Guardener" can be found inside a crate. Guess what Clover ends up running into just moments later...
    • During the ending sequence of the Neutral Route, upon encountering a seemingly alive Martlet in the nightmare sequence Flowey has initiated, "she" goes to hug Clover... As "her" eyes and beak are replaced with black voids for a brief moment before turning to normal, making it very clear something's wrong before it's revealed it's a fake copy that melts away when it's clear Flowey has found Clover.
  • Foregone Conclusion: The game is this by definition, since Asgore has six SOULs by the time Frisk confronts him, meaning that Clover is fated to die. Unless you do the Genocide ending.
  • Foreshadowing:
    • There are several hints as to Flowey's true nature:
      • Clover lands on a bed of golden flowers in the Dark Ruins. Unlike other patches of flowers in the game that make sense given context, these have no business being there. It's almost as if Flowey knew Clover would end up there.
      • If you wait around after falling down the hole, Toriel will eventually return with a rope to climb, but before Clover even reaches the top, it cuts back to the start of the game. For a split second, a small Flowey can be seen in the corner, indicating that he's resetting. He really doesn't want Clover to go with her.
      • Interacting with certain save points multiple times may make Flowey get annoyed. The same applies if you mess up multiple times during his tutorial.
      • Flowey makes sure that Clover is the only person who sees him. Whenever Clover is with someone, the save points remain, but he never shows up. Why would he feel the need to stay hidden if he was a good guy?
      • Flowey also is insistent on Clover heading to Asgore. Directly, with as little wait as possible. No stopping to help people, no messing around — just straight there. A friend would have patience.
      • Flowey also makes an allusion to his original self on the Genocide Route. After killing Axis, Flowey will berate Clover for his "angst".

        Flowey: "Ever heard of "don't bite the hand that feeds you"? But oh, "it's okay to bite Flowey because he doesn't have hands." Well, I used to!"

    • In the background of the Honeydew Shopkeeper the top shelf contains a bird figure, a star, a lightbulb and a bow. Which foreshadows the four major bosses of the Pacifist route
    • When talking to Blackjack in the Wild East, at one point he mentions how even ballet shoes can be dangerous weapons. While it may seem like a nod to Undertale, it actually hints at the blue SOUL human, who fought with ballet shoes, playing an important role in the Ketsukane family's backstory.
    • In the Steamworks, Clover and Ceroba find a "You Tried" award that was given to Chujin. Ceroba comments that Chujin never told her he got an award and praises him for receiving it, completely ignoring what kind of award it is, a first look at her blind faith in her husband.
    • When talking with Dina, she'll mention that she hasn't seen Kanako for a while.
    • A lighter example, but several monsters early on assume Clover is from the east. Then you get to the Wild East which is the Underground version of the Wild West, and suddenly the comments make perfect sense.
  • For Great Justice: Clover, whose virtue is Justice. The opening implied they went into Mt. Ebott in search of the other missing people who disappeared there, as their inventory initially starts with nothing but a missing person's poster.
  • Functional Magic: The monsters' attack and life force is explicitly stated to be magical. One of the reasons that humans and monsters are so different is that humans inherently can't use magic.
  • Game Within a Game: Mew Mew Love Blaster, a Shoot 'em Up you can play at the cafe in the Oasis Valley. It's not free, though, as each playthrough costs 3 gold.
  • "Groundhog Day" Loop: Flowey is the one in control of the ability to SAVE, and the Neutral Ending reveals that he's keeping Clover trapped in a time loop until they finally get the Pacifist Endings, and there's nothing Clover can do. Only by getting the Genocide Ending does Clover gain enough determination to override Flowey's ability to SAVE.
  • The Guards Must Be Crazy: Red keeps getting captured by the Royal Guard because they keep mistaking her for a human. She admits she keeps getting captured on purpose, almost subverting this trope, but then she says she does so in hopes the Guard will learn her face so they don't do that mistake. So far the Guard has failed to identify the person they've arrested countless times as the correct species. Martlet seems to be aware of this trope as she invites Red to join (much to Red's bafflement, cause it can't be THAT easy) and points out they even let her join.
  • Guide Dang It!: While you're killing monsters in a Genocide run, it's usually somewhat obvious that you should turn back if you hadn't exhausted the encounters yet, either if you're in an area where a boss fight would occur on a Neutral/Pacifist run or if the game warns you to turn back like in the Dunes. One would think it would apply similarly in Steamworks, where you can simply save next to the Furnace and go back to killing the robots. However, simply entering the control room where you would shut them off in Neutral/Pacifist (rather than the Furnace where Axis is located) will disable the encounters without warning the player at all, and since there's a save point in the next room, you can abort your run and not even know it until it's too late.
  • Heel–Face Turn: Like Undertale, you can do this: do something bad, then reset and not do the bad thing in the first place. You can also abort your Genocide run by either not killing all the monsters in an area, or by sparing certain bosses. Martlet's first battle in particular gives you the option to apologize.
  • He Who Fights Monsters: Clover, in a Genocide run. Their virtue is Justice, and they have come to the Underground to dispense justice on the monsters who killed the five human children and stole their SOULs. However, Clover then starts killing any monster, regardless of if they were involved in the killings or not, which eventually tallies close to the triple digits in terms of monster deaths. By the time you reach the Final Boss of the Genocide route, it's noted that the amount of proverbial blood on Clover's hands can't possibly be justified.
  • Hidden Eyes: Clover's eyes permanently disappear from their sprite during the Genocide route, once they kill every regular enemy within the Dark Ruins.
  • Honest John's Dealership: Mo, the travelling food seller, constantly tries to sell completely mundane and questionable quality food stuff as the best big thing. For example the first time you encounter him he tries to sell you, among other things, hot chocolate that got frozen, because hot and cold drinks are so last season.
  • Honor Before Reason: The Genocide route has two instances of this, with Clover on both ends of it:
    • The Snowdin fight against Martlet ends before you can kill her since she surrenders. Since Clover's LV isn't high enough for them to totally be consumed by vengeance yet, Clover lets her go.
    • When you get to the town in the Dunes, everyone has evacuated, except for Starlo. He admits he should hide with the others, but feels that that's not what a sheriff would do. He then challenges you to a "dual", where it turns out he didn't even have a real gun because he knew he'd lose anyway, which leads to his death.
  • Hopeless Boss Fight: The Post-Final Boss of the Flawed Pacifist route. If you kill Ceroba after the final fight of a pacifist run, Asgore kills you in the form of one of these. His attacks are dodgeable, but you can't fight back and never get to take a turn. If you survive long enough, the attacks can't be dodged.
  • Hope Spot: Asgore, as Undertale fans know, inadvertently created one, in declaring war on the humans after Chara's and Asriel's deaths and wanting six SOULs to cross the barrier, all the while unwilling to do the actual murder. Toriel calls him out for this and this ended their relationship.
  • Horrifying the Horror: If you go to the Steamworks alone, Flowey is completely creeped out by the overgrown laboratory and actually gets nervous the longer you stay there. The Alien Kudzu scares the crap out of The Soulless Botanical Abomination.
  • The Hunter Becomes the Hunted: Over the course of multiple different routes. On the pacifist/neutral routes, Axis will chase Clover and potentially Ceroba through a winding hallway in the Steamworks. On the genocide route, after Clover fatally wounds Axis at the start and follows him to the same hallway, the roles are flipped.
  • I Just Shot Marvin in the Face: You're able to accidentally kill Starlo in one hit during his boss fight whenever you make it through his slow-mo move. His final words is asking Clover to tell his parents that he'll be gone for a while.
  • Improvised Armour:
    • Many of the accessories serving as armor really shouldn't be able to do so, like the feather on your hat.
    • On a non-Genocide playthrough, Axis hands Clover a lid from a trash can to trick his programming into thinking Clover drew a weapon. He then complains when Clover proceeds to use the lid as a shield.
  • In-Universe Soundtrack:
    • While traveling the Dunes with Martlet, it's possible to talk to her and get an interesting tidbit on the battle music: In particular that when a monster focuses in during a battle, a music-like vibration echoes throughout, possibly heard by their opponent as well. She also theorizes if determined enough, humans could hear their own battle music as well.
    • At one point in the Wild East, an NPC mentions that the Feisty Five set up speakers around the town to play western-style music, with different variations in different areas, just like the music that plays in-game.
  • Infinity -1 Sword: By sheer statistics, Nail Ammo and Delta Rune Patch are the best items that are available with minimal effort, granting 10 points in the respective stat, with the ammo lying around in Steamworks and the armor being bought in the last shop; however, there are other items that might prove more useful depending on the playthrough, such as Silver Scarf's passive healing, Glass Ammo healing by two on a critical hit, or Silver Ammo's extra strong critical hits if the player can consistently land them.
  • Infinity +1 Sword: For ammo, the Friendliness Pellets, which are acquired late into Steamworks if Ceroba isn't with the player (though at that point, there's barely any fights to test them out on) or after the Ceroba fight on No Mercy Route, boasting 11 attack points, only rivaled by Silver Ammo's criticals. For armor, there is the Golden Bandana, acquired for bringing all the hidden golden items to yet another hidden room in Steamworks, boasting an amazing 12 defense points. Unlike the pellets, it is available on all routes, though the Optional Boss protecting it does not show up on No Mercy.
  • Insurmountable Waist-Height Fence:
    • How your paths are cut off in Hotland. At one point there's a blockade made by Micro Froggits, and on another path there's a rope with a note not to go under it.
    • In Steamworks it's impossible to move around the chairs or the trash bins. Then again, they may be stuck on the floor given the state of the lab.
  • Internal Deconstruction: In video game Undertale, Determination is an Arc Word that is shown to be one of the most admirable traits a human can have, and something monsters strive to have for themselves. Undertale Yellow takes that line of thinking and puts it through the wringer, especially with the Ketsukane family. Chujin is damn determined to be the scientist the Underground needs, but has none of the skill needed to back up his determination, with most of his experiments ending up with people and/or property getting harmed at best, and others ending up dead at worst. Ceroba is damned determined to vindicate her husband's experiments and theories he could never succeed in life, which causes her to be blinded to how incredibly dangerous they actually are and the very obvious, dangerous faults her husband had, which leads her to making downright boneheaded decisions. Kanako wanted nothing more than to help her parents anyway she could, which would result in her becoming a fallen down. While determination can be an admirable trait, too much determination over common sense can cause more problems in the long run.
  • Jaded Professional: Implied with the Janitor in the UG Apartments. In Undertale they look extremely depressed and incompetent, too busy cleaning their own mess, but here they're doing such an excellent job the floor is reflective and they look much happier. Clearly in between this game and Undertale the job took a toll on them.
  • Justified Save Point: The game is set after Flowey gained Determination (giving him the ability to save and load) but before he became fully sociopathic. Clover, unlike Frisk, doesn't have enough Determination to steal it from him unless they're doing a Genocide run and even then only in the ending, but Flowey is willing to create a save file for them, with the sparkling save points being created by Flowey so Clover can call him to save.
  • Kick the Dog:
    • The narration while inside Dalv's house pulls this on a Genocide run. The fridge is described as "tacky", Dalv's drawings are called "childish", and the organ in his room is described as "horribly out of tune".
    • The Neutral Ending sees Flowey murder Martlet and try to steal Clover's soul. He makes it clear this is nothing more than him deciding to punish them for Martlet convincing Clover to leave their quest and is simply a needless act of cruelty, as he could simply reset time without either of them even knowing. Despite knowing exactly how this is going to end, he continues doing so on each following Neutral Ending for no other reason than to make them suffer for defying him.
  • Kids Raiding the Wine Cabinet: The saloon in the Wild East serves "Adult Soda", but Dina refuses to serve Clover any. Clover can snag a bottle anyways from a trash can in New Home on a Pacifist run, or they can take one from a more spiteful Dina on a Genocide run. It notably doesn't get Clover drunk or have any negative effect on them, stated to just "taste like water".
  • Late-Arrival Spoiler: The game automatically spoils a few plot points of Undertale proper, due to being a prequel and assuming the player is familiar with that game. One big one is that not only is saving and loading an In-Universe power, but Flowey is aware of it and gained it before Frisk did.
  • Lighter and Softer: In a rather screwed up way, the Genocide Route ending of Yellow is this in comparison to Undertale's own. While Undertale has the Genocide Route end with Chara stealing control from the player and annihilating the world after everything is said and done, permanently tainting the player's file and future endings for performing said Genocide Route, Yellow has no such severe consequence for killing everyone, simply ending with Clover swiftly killing Asgore and taking his soul, and taking the other five human SOULs to the human surface.
  • Magical Accessory: Unlike Frisk, who changed clothing and weapons, Clover keeps their hat on at all times. Instead, they get various accessories that give buffs.
  • Maximum HP Reduction: In the battle against Ceroba during the Genocide route, she has access to red attacks that will decrease the player's max HP if they hit. Clover's max HP value will also gently pulse red if this happens.
  • Mental Time Travel: As in Undertale proper, this is how saving is explained. Unlike Undertale, however, Clover lacked the Determination to hijack it from Flowey (as their virtue is Justice instead), so instead Flowey does it for them.
  • Monochromatic Impact Shot: Martlet ends up on the receiving end of this in the Neutral Route, as everything cuts to black silhouettes on a white screen as Flowey murders her via impalement.
  • Mood Whiplash: In the Pacifist and Neutral routes; the Guardener battle is a rather lighthearted fight against a Comically Serious robot who orders the little robots to do her bidding. Once she's spared though, we get to see a very poignant cutscene of her realizing that the place she's in is long abandoned, her creator is no longer responsive, and she has no use anymore, prompting her to apologize to Clover and proclaim that she does not want to see what the world has become, then permanently going dormant.
  • Multiple Endings: Just like in Undertale, Yellow has three routes, each with different endings:
    • Neutral: After Martlet tries to get Clover to stay with her, Flowey kills her and reveals that Clover always died during when they travelled though the Underground the same way Frisk would/will, and therefore altered the puzzle in the ruins to send them to the Dark Ruins in an attempt to get them to Asgore. Flowey then tries to kill Clover, but after being unable to, resets back to the beginning of the game, urging Clover to make different decisions to get a better ending.
    • Pacifist: A fierce clash occurs with Ceroba, who's seeking to protect monsterkind at any cost, while also intending on killing Clover to use their soul to revive her late daughter Kanako in honor of her late husband Chujin's legacy. However, at the end of the fight, a Last-Second Ending Choice occurs in which Clover can decide whether to kill or spare Ceroba, resulting in two different Pacifist Route endings:
      • Flawed Pacifist: If Clover kills Ceroba, Starlo walks away disgusted at Clover and despaired with her death. Martlet decides to take Clover to see Asgore to try to talk things out. However, when it becomes clear that Clover and Asgore intend on fighting no matter what, a heartbroken Martlet leaves, and a Hopeless Boss Fight ensues where Asgore ultimately kills Clover, taking their SOUL. As Toby Fox's Word of God confirms that Asgore killed all six humans before Frisk arrived, this is the closest to a canon ending, although given that the game also reveals that Axis killed the human with the blue SOUL, the game may not be following this thread in the first place.
      • True Pacifist: If Ceroba is spared, Clover, after seeing the injustice monsterkind experience every day, gives up their SOUL to give them all hope, and to prevent reckless actions from risking more lives. Clover's SOUL is given to Asgore, Martlet quits being a member of the Royal Guard, and all of the remaining main characters give Clover a final send-off by putting their hat and revolver in a boat and letting it sail down Waterfall. And once all of the credits have rolled, we cut to the events of Undertale as Clover's soul hears Frisk calling for help, deciding to answer…
    • Genocide: Clover kills everyone and, after a hard battle against a determination-filled Martlet, reaches LV 20. Flowey gets mad, stating that the Underground would notice a super-powerful human running around and tighten security, and when he accidentally lets slip that he wants the souls for himself, Clover tries to kill him. Flowey attempts to Load his Save, but Clover is so powerful now that they have more determination than Flowey, and after Loading their own Save to prevent Flowey from attacking and running away, kills him. Clover then marches to Asgore's home, kills him, steals his SOUL, and takes the human SOULs with them back to the surface.
  • Musical Spoiler: In the Genocide route, every boss after Dalv gets a new battle theme unique to the route (except for El Bailador, who is optional). These new battle themes incorporate a motif from Enemy Retreating... except for Apprehension and Remedy, both associated with Martlet. For Apprehension, the expectation of the motif isn't established yet, but it's strange that it's absent from what seems to be the final battle... until you reach her second phase, at which point Retribution kicks in with that motif front-and-center, showing that it's finally time to kill her for real.
  • Mythology Gag:
  • Nice Job Fixing It, Villain!: During the first fight against Martlet on a Genocide run, she points out that if you hadn't attacked her when you did, she might have led you to where the others were.
  • No Ending: The Neutral route ends with Flowey murdering Martlet and attempting to absorb Clover, resulting in the pair being locked in a pointless, endless struggle inside Flowey's mind because Clover refuses to be absorbed but can't meaningfully fight back. Eventually, Flowey simply gets tired of Clover's resistance, acknowledges the struggle for the waste of time it is, and resets the timeline. Nobody's desired end goal is advanced, and the story gets no resolution this way.
  • Non-Standard Game Over: Multiple.
    • The first is an oddly non-lethal case; if Clover waits several minutes for Toriel where they fell in the Dark Ruins, she will actually return, hoisting a rope down for them to climb. Climbing up the rope will suddenly cause the game to glitch, a sprite of Flowey suddenly appearing to the side, and restart, forcing the player back to the opening and title screen. If the Neutral Ending is any indication, this very well could be Flowey resetting the timeline to prevent Clover from traveling with Toriel and dying.
    • The second happens much later in the Steamworks in a Neutral or Genocide route, where Clover obtains a glass of Acid as part of a puzzle. The Acid works as a regular item, and if the player so desires, they can make Clover drink it, which immediately kills them. Flowey is left utterly speechless.
  • No OSHA Compliance: The Steamworks are...not very worker safe, with seas of molten pink fluid, high areas with no guard rails, and emergency doors requiring passcodes that can only be obtained in really obtuse ways. While being out of commission for years and falling apart didn't help matters, it's implied it was already this way before that. Talking with Ceroba will make it clear she's not very happy with the arrangement.
  • Off the Rails: This is the end result of the Genocide route, averting Doomed by Canon. Despite Flowey's insistence that Clover will die no matter what they do, they manage to kill Asgore and pass through the barrier with the five human SOULs in tow.
  • Omnidisciplinary Scientist: Similar to Alphys in the main game, the Steamworks' scientists tend to dabble in multiple disciplines. According to its database, head scientist Oscar Rutherford has several text boxes' worth of accreditations, and Chujin Ketsukane is a roboticist and geneticist. Subverted in Chujin's case, as he wasn't particularly skilled in either field, with disastrous results.
  • Pacifist Run: Much as in Undertale proper, it's possible to complete the game without killing anyone. Every battle has a way to end it non-violently, and it's up to the player to figure out how. However, because this is a prequel and Clover is dead at the beginning of Undertale, it can be logically assumed that Clover is likely not making it out of this in one piece. It's also implied that a Pacifist run is the canon ending, since it's the only ending in which Clover's items are placed at the Waterfall (where Bratty and Catty find them), and the only one that hears Frisk's SOUL calling for help.
  • Personality Powers: According to Word of God, Clover's Justice has different abilities compared to Frisk's and Chara's Determination, which can be seen in each of the routes' final bosses with the exclusion of Asgore in Pacifist and the inclusion of Axis in Genocide, which manifests as Clover's SOUL flipping upside-down and firing laser beams — similarly to the Yellow SOUL mode in Undertale, but far more powerful. One difference, however, is that Clover can't save, and thus Flowey does it for you. At the end of the genocide run, however, Clover gains enough Determination to steal the power from Flowey and kills him.
  • Player Nudge: Reaching the road just outside the Oasis before exhausting the kill count on a Genocide run prompts one of these. "There are still enemies to bring justice on." If you don't turn back, then the run is aborted.
  • Plot Tunnel:
    • In a Neutral or Pacifist route, the entrance and exit to the Wild East are blocked off, keeping you trapped in the town while you progress through North Star's missions. The Dunes as a whole may qualify, since you can't go back to Snowdin until you reach the end of the area, where the Mail Whale will introduce travelling between mail stations.
    • On a Pacifist route, once you enter the Steamworks, you won't be able to freely backtrack until after you've discovered the secret in Ceroba's house. There are mail points in the Steamworks, but Ceroba won't let you use them, and once you've left the area, Martlet accompanies you while you look for the aforementioned secret.
    • And on a Genocide route, once you enter the Steamworks, the door locks behind you, meaning you can't leave at all.
  • Point of No Return:
    • Leaving the Dark Ruins is the first point of no return in the game, as you are unable to revisit once you depart. Flowey even removes his save points if you talk to him after the fight with Dalv, saying that there's no point going back there.
    • Because the Mail Whale doesn't show in the Genocide Route, you're also unable to revisit Snowdin once you leave.
    • Meeting Martlet on the roof of the UG Apartments locks you into the endgame. On Neutral, you begin the final boss battle against Flowey, while on Pacifist and Genocide you are no longer able to backtrack.
    • The computer room before the encounter with Axis is the last opportunity to abort a Genocide route, while the Axis fight itself is the last chance to abort a Pacifist route.
  • Post-Final Boss: After the Steamworks, you reach Hotland which, unlike in the original game where it was a full-fledged area, is featured with only a small portion (the end of the area and the UC Apartments) available and the rest closed off, and serves as the setting for the Neutral and Genocide final battles. New Home follows suit in the Genocide and Pacifist routes, as a series of hallways that lead to the conclusion of the respective routes (and the Pacifist final fight).
  • Posthumous Character: Chujin, who's mentioned a few times by Ceroba. We only see him via videotapes or flashbacks in the Pacifist route, or just a flashback in the Genocide route.
  • Pre-Asskicking One-Liner: On a Genocide route, Martlet has two of these punctuating her speeches for her two phases. At the beginning of the first phase, it's, "Clover... your terror... ends now!". And at the beginning of the second phase, it's a simple, "Good luck."
  • Prequel: Follows the story of the yellow SOUL that came before Frisk.
  • Present Absence: Despite Chujin being long dead, the actions that he took in life are what drive almost all of the main characters.
  • Promptless Branching Point: In the Dunes, if you head towards the Oasis without exhausting the kill counter on a Genocide route, the game will warn you about it. However, there is no warning in Steamworks, where the encounters will stop once you enter the control room, and there's a save point in the room right after it, meaning that you can accidentally abort the route and then save over it. This isn't helped by the fact that Flowey tells you not to bother killing the enemies here as they are robots (who aren't possessed by ghosts) and don't give out EXP.
  • Rage Breaking Point:
    • In the Genocide route, after Axis admits they were the one to kill the last human that entered the Underground, Clover completely snaps. Their LV shoots up 7 levels near-instantly, and they pay no attention to Axis pleading that they didn't want to before annihilating him with a laser from their SOUL. From this point on, everything Clover does is in full Tranquil Fury mode.
    • In the Neutral route, Flowey's friendly facade finally breaks when Marlet inadvertently derails his plans by asking Clover to live with her, resulting in him killing Martlet and attempting to take Clover's SOUL with a Battle in the Center of the Mind.
  • Railroading: For all that Flowey insists you get to Asgore in the Neutral route, it's literally impossible. The elevator leading to New Home in the UG Apartments (MTT resort) is occupied just like in Undertale, and the path leading to the CORE is blocked. You have no other option but to talk to Martlet.
  • Redemption Earns Life: Inverted in the genocide route. The only ending where Clover lives is the one where they've gained enough power from merciless slaughter to override Flowey's ability to SAVE, kills Asgore to take his SOUL, and leaves the Underground with the rest of the human SOULs in tow.
  • Retcon: While the game does its best to be as canon as possible, there's inevitably some contradictions:
    • In Undertale, it's indicated that a long time has passed since the last human fell into the Underground before Frisk did, to the point where the majority of monsters don't recognize them. In Undertale Yellow, flashbacks and various dialogue implies Clover jumped into the Underground around a year or two before Frisk at most, with Integrity falling into the Underground a couple years before that.note 
    • If one takes Toby Fox's Word of God statements as canon, all six of the humans made it to Asgore and died by his hands. In Undertale Yellow, the human that fell before Clover, the Blue SOUL also known as Integrity, was killed by Axis via a heavily implied Boom, Headshot!. The game goes with the interpretation that they died in Waterfall when Chujin mentioned that Axis hid the evidence in that area since that's where the Old Tutu and Ballet shoes can be found in Undertale, hidden in tall grass and behind a waterfall respectively.
  • Rewatch Bonus: On the pacifist route, when you're going through the abandoned lab with Ceroba, she is rather insistent that Clover continue on their path, keeping them from checking their mail under the reasoning that the royal guards are looking for them at the moment. Once you know that Ceroba was planning on killing Clover for their SOUL, it becomes apparent it's less about the royal guard finding them and more her trying to keep Clover from getting any outside hints that something may be up.
    • Dalv's dialogue before and during his boss battle where he acts as if he's met Clover before and thinks they want to "finish the job" makes more sense after learning that a previous human had attacked a monster in Snowdin during Chujin and Kanako's visit, with some hints strongly suggesting that Dalv was that same monster. Similarly, his mention of someone who kept giving him corn until they suddenly disappeared one day, also implied to be Chujin or Kanako.
    • A particularly dark example is a girl on the playground in the Dunes lamenting the fact that her friend who always played with her stopped appearing one day. When you find out about Kanako, this gets much darker.
  • Sadistic Choice: You want to screw destiny, defeat the bad guys, and save the humans? Then you have to watch Martlet slowly melt to death in pure fear after you went on a genocidal crusade.
  • Screw Destiny: Weirdly, the Genocide Route is framed as this, as Clover is able to avert their fate of being killed by Asgore and return to the surface with the other five SOULs. That said, don't expect the game to go easy on you for going down this route despite this.
  • Screw This, I'm Outta Here!: Most of the shopkeepers pull this on a Genocide run, with the exception of Dina, who simply refuses to sell to you, and Vendy, who is likely immobile, but is afraid of Clover and gives items for free. Flowey attempts this at the end of the run when his attempts to kill Clover fails after they override his ability to SAVE, but they don't let him escape.
  • Sealed Evil in a Duel: The Neutral Route final boss ends with Clover unable to defeat Flowey (as they're dead and inside of Flowey's mind), but too determined for Flowey to fully absorb them either. Flowey Defies this trope by realizing if this keeps on, they'll be fighting for eternity, so he just resets to try again.
  • Ship Tease: Can be invoked by talking to Ceroba with this exchange.

    Ceroba: "The truth is..."
    Ceroba: "I don't think i'll ever be able to move on"
    Ceroba: "You know, find someone else and try to be happy again."
    Ceroba: "I don't think anyone like him is out there."
    Clover: *Picks the option "Starlo?"*
    Ceroba: (Surprised expression) "!"
    Ceroba: (Changes to Sweating worried expression) "You're..."
    Ceroba: "You're serious?"
    Ceroba: (Sigh) "Well..."
    Ceroba: "Perhaps at one point in my life I considered it."

  • Shoo Out the Clowns: On a Genocide route, none of the Feisty Five aside from Starlo make an appearance because he made sure they were evacuated along with the other Wild East residents. Additionally, while you can still get the Golden Bandana if you've collected and held onto the gold items from each of the previous areas, there will not be a fight against Macro Froggit.
  • Shout-Out:
    • The Pacifist route final boss, Ceroba, is overtly Japanese in aesthetic in an otherwise Spaghetti Western inspired game, and (like the other final bosses) utilizes the Shoot 'em Up mechanics characteristic of the Yellow Soul, which might bring to mind the Bullet Hell genre codifier itself, Touhou Project. The battle theme that accompanies her second phase is also very reminiscent of ZUN's musical style. This is also the case for the Mew Mew Love Blaster arcade game.
    • The Neutral route final boss, Meta Flowey, uses different animation styles in various stages you have to complete to "beat" him. Several of them contain referneces
      • The "Clay" form uses a claymation style that heavily resembles that of Hylics. Flowey also drops gray eyeballs in this as one of his attacks that are very similar to the infamous Prunsel meme.
      • The carnivorous plants that Flowey attacks with in between phases closely resemble Piranha Plants, right down to attacking out of pipes and spitting fireballs.
      • In Flowey's "Polygonal" form, not only does the background music use the instruments from Ocarina of Time and Majora's Mask, but once Flowey's red petals are shot enough times, his face will turn red-tinted and skull-like, almost resembling a smiling version of the Moon from Majora's Mask, or even the popular depiction of Ben Drowned.
      • The "Organic" form is very similar to the Mom's Heart and It Lives bosses from The Binding of Isaac in it's artstyle and heart like appearance
    • A door in Steamworks is labelled with the number 427, referencing The Stanley Parable.
    • The detention room that Axis tosses you in the Steamworks has a black-and-white checkered floor and a suspiciously familiar table that features a monitor, a table fan, and a phone right next to a bunch of stale pizza, and interacting with the computer will prompt a quote about how nice it would be to have security cameras that monitor robots in the Steamworks, but that they were never installed. You even escape it through the vents, not unlike how the animatronics can attack the player in Five Nights at Freddy's 2. Unsettlingly enough, the room even has a jumpscare (itself featuring none other than the "Purple Guy" ICE-E's P"e"zza mascot from Deltarune) that shows up on the allegedly nonexistent security cam if the game has a FUN value of 16-19.
    • There's a suspicious arcade cabinet in Oasis Valley that's a clear Shout-Out to the Polybius urban legend, with a FUN value of 65-69 causing an agent to show up and take notes on it.
    • The Telly-Vis robot has an attack referencing the iconic "Bouncing DVD Logo" screensaver.
    • In the element-mixing room in Steamworks (Neutral route only), Clover can find a gold ingot whose sprite strikingly resembles the one from Minecraft.
    • Interacting with Starlo's rocket-shaped bed will prompt the line "(See you space cowboy)".
    • Many of the attacks of Macro Froggit resemble other video games. One puts you on a road while cars (with frogs driving them) drive past, resembling Frogger. Another has a frog on an Arwing from Star Fox shooting at you, wearing a headset that makes him vaguely resemble Slippy. Yet another has you attacked by a humanoid frog wielding a sword, resembling Frog from Chrono Trigger.
    • The eerie, slender figure that can be seen watching Clover out of the corner of the abandoned Bits n' Bites in a Genocide Route somewhat resembles and plays a very similar role to the Hell Valley Sky Trees.
    • One video game that can be found (though not played) has the label of Surface Tycoon, calling to mind the assorted Tycoon games that MicroProse was famous for.
  • Shows Damage: Unlike in the original game, enemies become visibly beat up if you attack them.
  • Silence Is Golden: After Clover kills Asgore on a Genocide run and absorbs his soul, there is almost no sound at all, except for some wind howling, as they take the other five SOULS and exit through the barrier.
  • Skippable Boss: Both Decibat and El Bailador can fail to show up if you exhaust the kills in their respective areas before reaching them. Neither will abort your Genocide run, though.
  • Stealth-Based Mission: In the Pacifist route, there's a room in the Steamworks where you have to find parts of a code to unlock the elevator in a darkened room while Axis is looking for you. If you get caught, you'll have to travel back through a few rooms to try again.
  • Stupidity Is the Only Option: One room in the Steamworks has a save point, some items you can pick up, and flowers that will get trampled if you walk over them. You might wise up and reload your save so you can walk around them instead, knowing that there is likely to be an enemy nearby that won't be pleased if you tread on them, but then you find some flowers that you can't walk around, so you have no choice but to trample them and end up in a boss battle anyway.
  • Swapped Roles: When playing through the Steamworks on a Genocide route, this is utilised in a dark manner in contrast to the Pacifist/Neutral route.
    • Instead of Clover tumbling down a trap door in their first confrontation with Axis, the robot uses that same trap door to make his escape when he realises just how big a threat the human child is.
    • Likewise, instead of Axis chasing Clover through the facility, Clover instead chases Axis through the hallways.
    • The Pacifist/Neutral route had Axis giving Clover a bin lid as the equivalent of a weapon to exploit the loophole of his programming. In the Genocide route, however, he uses that bin lid to defend himself from Clover's onslaught.
  • There Is No Kill Like Overkill: During the Genocide route. Much like in the Genocide route from Undertale, Flowey meets his fate in a similar way here. After realizing that Clover is overwriting his power to SAVE, Flowey has a Villainous Breakdown where he goes Laughing Mad and gives Clover a "The Reason You Suck" Speech. After Flowey starts laughing, Clover shoots Flowey a total of eight times in a row, causing Flowey to just slump over dead with barely anything left of his body by the time Clover is done firing.
  • Tongue on the Flagpole: There's a NPC in Snowdin whose tongue is frozen to a lamp post, and asks for hot coffee to melt it off. But not too hot, otherwise he calls you out for trying to burn his tongue altogether. It's possible to free his tongue by obtaining the right item though a Chain of Deals.
  • Troubled Backstory Flashback: Each of the three routes has one of these during their final battle, each shedding new light on a focus character of the route:
    • The Pacifist Route reveals the tragic true nature of Ceroba after the final stretch of the route had been building up the Ketsukanes' backstory, in particular the day of Chujin's passing, as well as her failed attempt to complete Chujin's work and legacy resulting in her daughter Kanako falling down.
    • The Genocide Route reveals a bit more of Martlet's past, of which the player can read some of in her diary at her house (Albeit with the final entry torn out) specifically her conversation with Chujin the day she revealed she joined the Royal Guard... And the day she decided to enter Alphys' Lab to retrieve a vial of Determination as a failsafe for a human encounter, revealing Chujin's warnings and prejudice against humans stuck to her to an extent, and in this route, to a very reasonable extent.
    • Notably, the Neutral Route has this for both Clover and to a lesser extent Flowey, revealing that all of Undertale Yellow was engineered by Flowey because Clover just kept dying on the path that Frisk would eventually walk, or wouldn't be able to actually get to Asgore (In particular settling in with Toriel) before Flowey decided to reset the timeline for another attempt. And on Flowey's end, a brief intermission between the phases shows Flowey's perspective of constantly living life after life with all the power he has, and his reactions to the attrocities he both endured and caused in the past before becoming the maniacal flower he is today.
  • Unstoppable Force Meets Immovable Object: The Neutral Route Final Boss eventually devolves in into Clover being unable to kill Flowey but Flowey likewise being unable to completely crush and absorb Clover either. Flowey realizes this is a waste of time, as the only outcome is the two fighting for eternity, so he resets because he's not having fun anymore.
  • Video Game Cruelty Potential: In addition to the Genocide route and its usual entrappings, there's a scene in the mines from the Pacifist and Neutral routes where Clover finds a fearful miner who wants to report lost TNT to the foreman, but lost his hard hat and thus cannot go outside. If they go just a screen down, they'll find the miner's hat, who they can push towards him. Despite how simple this is, there's still the option of not going through with it; if this happens, the Pacifist Route credits will have a scene of all the other miners having fun while the lone miner, clearly fired, stands off to the side and sheds a Single Tear.
  • Video Game Cruelty Punishment: Going on a Genocide route leads to this, naturally. It pulls this in a few ways:
    • Every boss fight except for Dalv is harder to deal with here than in a Neutral or Pacifist run.
    • You can only steal one of each item from the shops, limiting your healing options severely.
    • Even if you haven't exhausted Snowdin's kill counter by the time you get to the resort, the NPC that you'd give the coffee to is gone, meaning you can't complete the Chain of Deals to free Slurpy from the flagpole note 
  • Weird West: The main premise of the game. The "Wild East" in particular is where you'll be spending most of your time.
  • What Measure Is a Non-Human?: When performing Genocide in the Steamworks, Flowey calls out Clover for "wasting time" killing the robots instead of just progressing forward for this reason; viewing the robots as "barely concious" heaps of metal not worth going out of the way to kill, unlike the Monsters.
  • Wham Line: At the end of a Neutral route, after Flowey kills Clover and absorbs their SOUL, it's revealed that this isn't anywhere near Clover's first run:

    Flowey: You see, I've been watching you for a while.
    Flowey: Gosh, what run is it? Gotta be in the hundreds.

  • You Have GOT to Be Kidding Me!: Flowey says this when their meeting near the Oasis is cut short by Martlet's arrival.
  • You Monster!: Martlet actually pulls an Inversion during the first fight on a Genocide run, pointing out that you have to be a human because of your cruelty and your hat.

Somebody calls for help... You answer the call.