To enable all characters in multiplayer mode, enter the password OMGTKKYB. That, as any South Park fan will know, stands for "Oh My God, They Killed Kenny! You Bastards."
All Weapons
For all weapons, enter the password FATKNACKER.
Big Head Mode
For big head mode enter the password MEGANOGGIN at the Cheat menu.
Bonus Characters
To access these characters in multiplayer mode, enter one of the passwords below.
veggieheaven = Skinny
cheatingisbad = Mr. Mackey
elvislives = Bar Brady
outrage = Big Gay Al
hawking = Ned
slapupmeal = Starvin Marvin
phaert = Phillip
raft = Terrance
dorothysfriend = Mr. Garrison
lovemachine = Chef
checkataco = Wendy
fishnchips = Pip
kickme = Ike
allwoman = Mrs. Cartman
goodscience = Mephisto
staringfrog = Jimbo
majestic = Alien
Invincibility
For god mode enter the password ASSMAN.
Level Select
To choose your starting level enter the password THEEARTHMOVED. After activating this code, start a new game and pause it. You may now enter the Level Select menu.
Master Cheat
To unlock all codes at once, enter the code BOBBYBIRD at the Cheats menu.
Pen and Ink Mode
For Turok's famous "pen and ink" mode, enter the password PLANEARIUM.
Unlimited Ammo
For unlimited ammo, enter the password FATTERKNACKER.
View Credits
To view the credits, enter the password "screwyouguys".
All Characters in Multiplayer ...