Killer Instinct Cheats

Fight your way up to Eyedol, then let him kill you. At the game-over screen, let the timer run down and then go to "Practice", pick your character, then you'll be practicing against Eyedol.

In VS mode, when you run out of life and your opponent has the opportunity to finish you off, start hitting random buttons like crazy. There is no specific sequence. If you manage to hit the buttons fast enough before your opponent hits you again, you will come back to life with only a sliver of health, but your attack power will be enhanced greatly. If you get hit again, it's over.