Debug Mode  -  At the main menu hold x,y,z,l, and r for about 15 seconds until input info on appears at the bottom of the screen. During the game there will be some debugging info at the top of the screen.

All weapons  -  Pause the game and press Z, X, X, Z, Y, Z, Y, X, Y. 

God Mode  -  Pause the game and press X, Z, Z, X, Y, X, Y, Z, Y. 

Level select  -  At the MAIN MENU screen press X, Y, Z, Z, Y, X, Y, Z, Y. 

Turok Style Control
Pause the game at at any time and press Y,Y,Z,Z,X,X,Y,X,Z for Turok style controls. Here are the controls:

A:open door/Drink/Action
B:Backward
C:straf right
X:use item
Y:straf left
Z:Walk Forward
L:Shoot
R:Jump
D-padUp/Down: Select item
D-Pad/Left/Right:Select Weapon

How to get the hidden game "DEATH TANK Zwei"  -  Load one time the game with a saving of EXHUMED or QUAKE in the memory. "DEATH TANK" will appear on the main menu. If you haven't got EXHUMED or QUAKE, you can get DEATH TANK Zwei if you shoot and destroy EVERY toilet and urinals in the game (except the giant one at stage UREA 51) and finish the game. The hidden game should then appear. 

No Monsters  -  At the "Skill Level" screen enter Z, Z, X, X, Y, X, Y, X, Z and the new skill level "No Monsters" will appear.