All codes entered at main menu screen. The cheat will flash at the top of the screen if entered correctly:
Flame On Mode (Character models on fire): Circle, Triangle, Square, Circle, Triangle, Square
Hot Hands Mode (Punch enemies to set the on fire): L1, L1, Circle, Square, Triangle, L1, L1
Invulnerability Mode: L1, R1, L1, R1, L1, R1, L1, R1
Small Heads: L1, L1, R1, L1
Big Heads: R1, R1, L1, R1
Exploding Fist (enemies explode when hit): R1, R1, Triangle, Square, Circle, R1, R1
Liquid Metal: Square, Triangle, Circle, Square, Triangle, Circle.