Cheats
When you start the game press A, B, Y, and X on controller 2. Then press A, B, Y, and X on controller 1. Now you'll get a number in the upper corner. Pressing A or X gives you invincibility, pressing B gives you no damage, and pressing X gives you unlimited ammo.
Code
Write "overgame" in the password menu. Then you come to the final level.
