Mortal Kombat 2

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.
Information in this section was contributed by zin21wall.

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.

Hint: Sub-Zero: Easy uppercut against Kung Lao:
When facing Kung Lao, attempt to freeze him. He will use his teleport to avoid it and get behind you, but will not attack in the process. Do an uppercut (Down + High Punch) immediately after performing the freeze for an easy hit. This works best when you attempt the freeze at long range.
Information in this section was contributed by Codo.