Hazza'rah is an undead type boss. His abilities of note include a chain mana drain, illusion summoning, and an area of effect sleep. He has an extremely small (approx. 5000) mana pool for a boss.
Mana Burn: Hazza'rah casts an AoE mana burn. This appears to chain through raid members. He cannot use this attack if he has no mana himself.
Illusions: Hazza'rah periodically summons three illusions. These can look like a felguard, an abomination, a giant lasher, or a devilsaur. Each spawns targeting a member of the raid and will attack that person unless intercepted or killed. These illusions deal physical attacks that hit for approximately 5000 damage before armor mitigation. Illusions are immune to area of effect attacks, but they only have 500 health.
Mass Sleep: Another periodic attack on the raid, Hazza'rah puts all opponents within range to sleep. This combined with the damage from the illusions can get messy.