Play as Whack Angus
Unlock all modes (Smack Attack, Flag Rally, Gate Relay), then win all three levels in the Desert world in each one (total of nine). After completing the last level, Whack Angus will be unlocked as a playable character. His personal weapons are throwing Butchering Knives.

Everything
Enter SUSIE! as your name to unlock everything but the fanplastic cheat.

Plastic
Enter FANPLASTIC as your name to see plastic rendering.

Unlock Space Stages
Enter BRAINSALAD as your name to unlock the space stages.

Big Head Mode
To activate Big Head Mode, press L + R + UP during gameplay.

Have Hazard Weapons
To have hazard weapons, enter your name as HAZARDOUS.

Have Melee Weapons
To have melee weapons, enter your name as MELEEDEATH.

Have Movement Power-ups
To have movement power-ups, enter your name as MOVEITNOW.

Have Personal Weapons
To activate this cheat, enter your name as UNIQUEWPNS.

Have Ranged Weapons
Enter your name as GUNSMOKE! to have ranged weapons.

Invinicibilty
To become invincible, name your character CODY.

Pen-Drawn Graphics
To see this cool effect, enter your character name as PENCILS.

Unlock Almost Everything
Enter PITA as your name to unlock nearly everything in the game.

Unlock Characters/Worlds
To unlock the various character/world combos, enter your name as one of the phrases below:
EARLSPLACE: Count Earl/Transylvania world
WHACKLAND: Whack Angus/Desert world
TWRECKSPAD: T. Wrecks/Jungle world

Unlock FMVs
To unlock all FMVs enter your name as MULTIPLEX!