Cheat Menu
Any time during the game, pause it and press A and Left, B, B, A and Right, B, B, A. Unpause the game, and the words 'Cheater!' will appear on the screen. Up comes a menu which lets you select your level, give yourself infinite energy and check the map of any level.
Contributed By: stonedwal.

Extra Life
At any time, pause the game and press B and Up simultaneously, then press B, A, C, A, A, A, A. You will hear Earthworm Jim say ''Cheater! Wheee Doggy!.'' When you unpause the game, you will see that you now have an extra life. You can perform this code as many times as you want.
Contributed By: Retro.

Level Skip
Begin your game, take controller one and press START to pause at any point, Now press A, B, B, A, A+C, B+C, B+C, A+C. You'll skip to the next level.
Contributed By: ATadeo.

Refill the plasma gun
At any time, pause the game and press C and Down simultaneously, then press A, B, C, A, B, A, C. You will hear Earthworm Jim say ''Cheater! Plasma!.'' Now when you unpause the game, you will have nine plasma shots. You can do this as much as you want.
Contributed By: Retro.

Skip to the end of the game
Pause the game, and press A+C, A+B, C, C, B, B, A, A. You will hear Earthworm Jim yell ''Cheater'' and you will be brought to the ending scene of the game.
Contributed By: masumane2.