Play as Alien:
To play as an alien enter L, R, L, R, and Z at the title screen.

Play as President Weller:
To play as President Weller enter: L, R, L, R, and start at the title screen.

Extra Mode:
Beat the game under Ultimate. Then at the Title screen, press L, R, L, R, A.

Learn more fighting abilities:
A lot of life chargers are required for this trick. You have to fight the mutants to learn different types of fighting moves. Fight one over and over again by going back into the room. Sometimes the best thing to do is to allow a mutant hurt you first. A "bing" sound will indicated that you have learned a new fighting ability. Do not forget to save the moves.

Avoiding fights:
You do not have to fight all enemies. You can run past them, or you could get across pits with enemies by jumping in the pit, running to the other side, and jumping out.

More Fighting Abilities:
Find any spot with a savegame area near one of those yellow things that guys keep coming out of, fight, get hit, or grapple, and everytime you hear a ding you have learned a new skill. Also this is great for upping your offense and defense and will work with a lot of powerups too.

Full power and overall advantage in fights:
When you walk into some rooms they will contain people that who you have to fight. To get the overall advantage over them, allow them chase you around the room until you get behind them. When you get close enough, "Advantage" will appear at the top of the screen. Not only will you have the advantage, you will start with full power and will take more of the creature's life away since you attacked from behind.

Open cheat mode:
Beat the game. At each saving point save, and restart the system. Change the resolution after each time you do this. (note: you must start with resolution set on "high res. letterbox" then cycle up from there.)This will add a cheat menu at the title screen. There is: Invincibility - on/off
All moves - on/off
All items - on/off
No key renewing - on/off
Play as any monster - select
Play as Alien - on/off
Play as Pres. - on/off
Level select - 0-0