Death Jr. 2: Root of Evil

All weapon upgrades:
Pause the game by pressing START, then hold L and press
Up, Up, Down, Down, Left, Right, Left, Right, X, O.

Activate Invincible mode:
Pause the game by pressing START, then hold L and press
Up, Up, Down, Down, Left, Left, , Right, Square, Triangle.
When you exit the start menu, "Can't touch this" message
will appear to confirm correct code entry.

Infinite ammo:
Pause the game by pressing START, then hold L and press
Triangle, Triangle, X, X, Square, O, Square, O, Right, Down.

Restore ammo:
Pause the game by pressing START, then hold L and press
Triangle, Triangle, X, X, Square, O, Square, O, Down, Right.