Limbo is an afterlife plane of existence originally mentioned in Roman Catholic doctrines and scriptural ideas during the Medieval era. Derived from the latin world "limbus" (meaning edge of the world), Limbo is one of the distinct parts of the Underworld, where the people, who died in their previous life, are sent to spent eternity without being assigned to Hell. In modern fiction, Limbo passed on as a source material including the Don Bluth's animated film Anastasia, where it depicts Rasputin spending eternity on Limbo after his death at St. Petersburg, before he would ascend to the surface to kill Anastasia Romanov.
Regarding the villain tournaments, Limbo appears as one of the afterlife planes of existence including Hell, the Spirit Realm, and the Netherworld, with the Don Bluth's film being used to represent its existence.