Cheat mode:
Highlight the "Done" selection on the options screen. Press Left, Down, Right(2), Down, Left(4), Right(3). More game options will be displayed.

Random fighter:
Highlight Liu Kang and press Up + Start at the character selection screen.

Fight against Jade:
Select single player mode. Win any round of the match just before the question mark using only Low Kick and the D-pad.

Fight against Noob Saibot:
Win 25 consecutive two player mode matches.

Fight against Smoke:
Quickly press Down + Start when Dan Forden appears on the Blue Portal stage.