Cheat Menu:
Access the "Enter Cheat" Option from the Title Screen, or by pausing the game. Enter the following codes you want to use:
CMGTSMMGGTS - all weapons
BLLTSRRFRND - unlimited ammunition
DLKTDR - black and white wireframes
SNFFRR - Disco Mode
FRTHSTHTTRLSCK - unlimited lives
THBST (cannot be entered while paused) - Gallery
FDTHMGS (cannot be entered while paused) - Credits
THSSLKSCL - Spirit Mode (invinciblity and slow-moving enemies)
After entering the codes you want, move down to the Enter command and press Start. The result will appear on screen. Press Start to OK the command. Now choose "Exit". Back on the Pause Menu, a new option called Cheat Menu will appear. Access this to get another menu which allows you to turn on the cheats you have already entered. Exit when you have finished and start or resume your game to have your chosen cheats activated.
Robins Cheat:
Begin player a game and pause the game. Access the "Enter Cheat" option and access it. On the Cheat Code Screen, enter RBNSMTH. This will give you "Robins Cheat" which turns on mutiple cheats (invincibility, unlimited ammo, all weapons, Big Head Mode, etc.).