Best of three

According to the Fourteenth Doctor, "best of three" was "an inviolable rule" that two players who were one-all were compelled to follow. The rule stated that the two players must have a third and final game to determine the true winner between them after two previous games resulted in a stalemate.

The Doctor enacted the "best of three" rule shortly after he lost a game of Cut against the Toymaker in 1925 Soho, pointing out that their tally was equal after he had won their first game "many years ago". The Toymaker then fled to 2023 for their final game, which ended up being a game of catch between the Fourteenth Doctor and the Fifteenth Doctor, in which the Doctors emerged victorious. When the Toymaker tried to bring up a technicality to excuse his loss, the Fifteenth Doctor evoked the "best of three" rule to cement his defeat. (TV: The Giggle ^[+]Russell T Davies, Doctor Who 2023 specials (BBC One and Disney+, 2023).)

When Christine Summerfield got the Horror to agree to a game of scissors paper stone for the fate of the Earth, she prompted if they could do "best of three" and it agreed, saying "why not?" (PROSE: Dead Romance)