LEFT, RIGHT, LEFT, RIGHT, RIGHT, LEFT

You will be taken back to the game, this time you will have 999 ammo.

Full Health
During gameplay you can press the Start button and pause your game. Now press:

DOWN, DOWN, DOWN, LEFT, UP, RIGHT.

You will be taken back to the game with full health.

God Mode
During gameplay you can press the Start button and pause your game. Now press

LEFT, LEFT, RIGHT, RIGHT, DOWN, UP.

You will be taken back to the game, but this time you cannot be injured.

Skip Current Level
During gameplay you can press the Start button and pause your game. Now press:

UP, DOWN, LEFT, RIGHT, RIGHT, LEFT