The cheats located below are from a few different sources, and I have included them at the bottom of the page. Those looking for PAR (Pro Action Replay) Codes, they are at the VERY bottom of this page.

INSTRUCTION BOOKLET CORRECTION:
Do not enter in the suicide code in room C-4 as instructed in the book. If you do, you will die!

SECRET INVINCIBILITY:
In room C-3, you can become invincible. Before you go into room C-3, collect the Zillion Power from room A-6. This will allow you to open the containers that are present. After you have the Zillion Power, enter the room and you will see an elevator next to an energy barrier.

Get in the elevator, reach out and touch the energy barrier, while pressing down on the Directional Pad. Repeat this, until your energy drops to zero. If this is done correctly, the bottom of the elevator will fall out, and you will be invincible.

NOTE: Once invincible, the pause button will do no good, which means you will not be able to change characters.

DEFEATING THE DRAGON:
After you exit the Computer Room, you will face a Dragon. To defeat him, shoot him in the mouth approximately twenty times. You will know that you are hitting him, because he will flash yellow.

NOTE: After the dragon is destroyed, re-enter the computer room, and re-input the suicide command. This will allow you extra seconds to escape. In addition, it may be useful to make a map of the exact way out, so you won't waste time getting lost!

EXTRA MESSAGES:
If you enter the suicide code in rooms D2 and G4 you will get a special message.

CONTINUE CHEAT:
Press buttons 1, 2 and Up on the joy pad after you've died. You can now continue on from where you left off.

 

Pro Action Replay codes
The code will only work with a new game, loading a Emulator Save State will not allow this code to work, you freakin' biters. Buy the game! You'll also notice that no matter what your MAX Health grows to be, you will never go above (or below) 700 HP. Just keep that in mind please.

00c14370 Infinite energy