For this next game, all cheats codes must be entered at main menu screen. The cheat will then flash at the top of the screen if you entered it correctly.
"Flame On" Mode (Character models on fire): B, X, Y, B, X, Y
"Hot Hands" Mode (Punch enemies to set them on fire): X, B, Y, L, L
"Invulnerability" Mode: L, R, L, R, L, R, L, R
"Kamikaze" Mode (Explosive bullets): L, R, White, Y, B
"All Levels Unlocked": X, Y, White, White, X, Y, White, White
"Infinite Hero-time": B, X, Y, White, L, R
"Pin Heads": L, L, R, L
"Big Heads": R, R, L, R
"Exploding Fist" (enemies explode when punched): B, X, R, R
"Liquid Metal": B, Y, X, B, Y, X
Unlimited Ammo
At the main menu, enter this code to get unlimited ammunation: White X4, L, R.