Cloaking Device
To clock yourself while playing, hold Triangle and press Square, Circle, Circle, Square. Release Triangle, then hold X and press Triangle, Triangle. Release X.
Maximum Ammo To enter this code you have to first press START then highlight "Music Volume." Once that's done, follow these steps:
Maximum Health Highlight "REVIEW MISSION", hold SQUARE, and press CIRCLE, X, TRIANGLE. Release SQUARE, hold CIRCLE, and press SQUARE, X, TRIANGLE. The word "Cheater" should appear at the top of your screen.
Secret Level In the Throg Breeding Facility you'll find a secret entrance to the "Lost City". Look for it in the lower right-hand corner of the map. You'll need to break through three or four secret doors to find this exit, but it's well worth it.
Shield Press and hold RIGHT, then press CIRCLE, SQUARE, TRIANGLE. Release RIGHT and hold LEFT, then press SQUARE, CIRCLE, X. Release LEFT and unpause the game to activate your shield. If you did it right, the word "Cheater" will appear.
Speed Up For a burst of speed while playing, hold UP and press TRIANGLE, TRIANGLE, TRIANGLE. Release UP then hold DOWN and press X, SQUARE, CIRCLE. Release DOWN to complete the code.