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
Hero mode
Press L + Y with a full special meter.
Ride the elevator
At Nakatomi Plaza, after riding the painter's elevator, open the elevator with the surprised guard and ride it to the broken doors two floors up. Press the "Down" button and get out quickly. You will be able to run and jump through the broken doors onto the elevator, and use the buttons to ride from the top. You can even shoot out the elevator's roof panels to go back into the elevator.
Unlimited Ammo
At the main menu, enter this code to get unlimited ammunation: White X4, L, R.