Enter any of this batch of cheats at the main menu, after you have entered them a message will appear on the screen which will confirm correct code entry...
Invincibility:
L1, R1, L1, R1, L1, R1, L1, R1.
Unlimited ammo:
L2(4), L1, R1.
Big head mode:
R1(2), L1, R1.
Small head mode:
L1(2), R1, L1.
Pin head mode:
Square, Circle, Triangle, Square, Circle, Triangle.
Exploding fists:
R1(2), Triangle, Square, Circle, R1(2).
Hot fists:
L1(2), Circle, Square, Triangle, L1(2).
Liquid metal textures:
Square, Triangle, Circle, Square, Triangle, Circle.