Fight as Goro:
Enable the "Cheat menu" code. Highlight "Hidden" at the bottom of the character selection screen, then hold L + R and press Up, Left, A.
Fight as Sektor:
Enable the "Cheat menu" code. Highlight "Hidden" at the bottom of the character selection screen, then hold L + R and press Up(4), Left(4), A.
Fight as Noob Saibot:
Enable the "Cheat menu" code. Highlight "Hidden" at the bottom of the character selection screen, then hold L + R and press Up(2), Left(4), A.