Killer Instinct

Double Speed

As soon as each player has selected a character, hold Right on the joystick and simultaneously press all three Punch buttons. (In a one-player game, the first player must do this with both controllers.) Hold these buttons until the prefight match screen appears and release them after you hear the swooshing noise for the second time. This code doubles the normal spped of the game, but it must be re-entered with every new match.
Play as Boss
To play as Boss, push the joystick Up four times, then Forward, Up, Down at the Combo Select Screen. Now push Quick Punch.
Play as Eyedol
Select Riptor, and hold Left while pressing Quick Punch and Kick, when the Versus screen appears, immediately change to holding Right and pressing Medium Punch, Fierce Punch, and Fierce Kick. The game should then say "Eyedol."
Shrink Players
On one of the platform stages (i.e. Cinder's stage), play as Fulgore. Back the other player to the edge of the platform, and start a combo, ending it with a teleport (B, D, DB + Fierce Kick). Now when you press either side's Start button, you'll shrink that player. NOTE: This will only work on machines before version 1.5 of the game.

Other Cheats

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Marvel Super Heroes vs. Street Fighter
Killer Instinct 2
Crazy Taxi
Vampire Savior 2
Virtua Striker 3
Planet Harriers
Aqua Jet
Bubble Symphony
3do
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Gameboy
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GameCube
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Nintendo N64
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Killer Instinct Game Cheat Codes