Mortal Kombat 2

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

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.