Cheat mode:
Begin game play with the screen resolution set at high resolution letterbox. 
Use every save point during game play. Reset the Nintendo 64 and toggle the 
screen resolution to the opposite setting after each save. A cheat menu with 
the following options will be unlocked at the title screen: invincibility, 
all moves, all items, no key renewing, play as monster, play as Alien, play 
as President, and level select.

Play as President Weller:
Successfully complete the game under the ultimate difficulty setting. Then, 
press L, R, L, R, Start at the title screen. A sound will confirm correct 
code entry. 

Play as Alien:
Successfully complete the game under the ultimate difficulty setting. Then, 
press L, R, L, R, Z at the title screen. A sound will confirm correct code 
entry. 

Extra mode:
Successfully complete the game under the ultimate difficulty setting. Then, 
press L, R, L, R, A at the title screen. A sound will confirm correct code 
entry, and the word "Extra" will appear at the lower right corner of the 
title.

Learn more fighting abilities:
Note: 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.

Avoid shots:
When in a battle with an opponent that shoots (but does not spray, spits, 
or blows), you may get a choice to walk, guard, or counter when he fires. 
Walk into your opponent, and his shot will usually miss you.

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.