Paper Mario: TTYD Theater is where every battle in Paper Mario: The Thousand Year Door takes place. As its name would suggest, it is a theater where Mario, his partners and his opponent(s) take turns attacking each other on the stage, battling in front of an audience consisting of Goombas, Koopas, Hammer Bros. and various other characters.

In M.U.G.E.N, Paper Mario: TTYD Theater has been made by Luneth. All the stage's elements are ripped from Paper Mario: The Thousand Year Door. It is actually multiple stages in one, as it comes with many .def files for almost every different scene in the game.