All ammunition
Press pause during gameplay and press Left, Right, Circle(3), Right, Left
All Weapons
Press pause during gameplay and press Left, Circle, Right, Square, Right, Left.
Invincibility
Press pause during gameplay and press Circle, Left, Right, Circle, Square.
Level Select
Save your game and return to the main menu. Then select "resume game" option, and highlight your prviously saved game and press Up, Down(2), Up, Left, Up, Right, Down
Level Skip
Press pause during gameplay and press Up, Down, Left, Right(2), Left, Circle
Fatboy Mutator
Press Circle(3), Up, Down(2), Up, Circle(3) at the title screen. Select the multiplayer mode and choose the "Mutators" option and choose "Fatboy Mutator". This follows the popular UT mod, the more kills you get, the fatter you get, and less kills, more you get killed, the skinnier you get
Stealth Mutator
Press Square(2), Circle(2), Square(2), Circle(2) at the title screen. Select the multiplayer mode and choose the "Mutators" option and select "Stealth Mutator"
Big Head Mode
Press Left, Right, Left, Right, Left, Right, Circle(3) at the title screen. Select the multiplayer mode and choose the "Mutators" option and select "Big Head Mode"
Firewire Multiplayer
First and foremost this requires a "Firewire Hub" and mutliple PS2s and copies of UT. Use 4 pin to 6 pin Firewire cables to connect the PSs2 to the firewire hub. . Pause the game in the two player multiplayer mode and press Left, Circle, Left, Right, Square, Right. Then have all players press start
Bonus Levels
Complete the game on the inhuman difficulty setting.
