Jungle world
Enter the character selection screen, select "Load", then enter "TWRECKSPAD" as a name.
Space world
Enter the character selection screen, select "Load", then enter "BRAINSALAD" as a name.
Ranged weapons
Enter the character selection screen, select "Load", then enter "GUNSMOKE!" as a name.
Movement power-ups
Enter the character selection screen, select "Load", then enter "MOVEITNOW" as a name.
All FMV sequences
Enter the character selection screen, select "Load", then enter "MULTIPLEX!" as a name.
Big head mode
While playing a game, hold L + R + Up.
Play as Brian The Brain
Win Smack Attack, Gate Relay, and Flag Relay in all three levels of the Space world to unlock Brian The Brain.
Play as Count Earl
Win Smack Attack, Gate Relay, and Flag Relay in all three levels of the Transylvania world to unlock Count Earl.
Play as T. Wrecks
Win Smack Attack, Gate Relay, and Flag Relay in all three levels of the Jungle world to unlock T. Wrecks.
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.
Additional FMV sequences
Finish Smack Attack, Gate Relay, and Flag Relay with each character to unlock additional FMV sequences.
Unlock Everything
Enter ENCHILADA! to unlock everything as your name when creating a new profile.
Melee Weapons
Enter the character selection screen, select "Load" then enter MELEEDEATH as a name.
Plastic Graphics
Enter the character selection screen, select "Load" then enter "FANPLASTIC" as a name. Enter the event selection screen and highlight "Smack Attack". Press Down and select the "Event Settings" button. Then, select the "Options" button and select the "Rendering Modes" button. Change this option to "Render: Plastic". The message "Current mode: plastic" will appear. Return to the even selection screen, then proceed to select a level and begin game play. To return to normal, repeat the steps and choose the cartoon renderer at the "Rendering Modes" screen.
Personal Weapons
Enter the character selection screen, select "Load" then enter UNIQUEWPNS as a name.
Unlock Everything Except Movement Power-ups
To enter this code, you have to have a memory card in slot A. Choose Create/Load and start a new game. Enter your name as PITA and start playing.
Susie knows best
To enter this, you have to have a memory card in slot A. Go to Create/Load and select new game. Enter your name as SUSIE!(don't forget the !) and you will have unlocked everything but the ending movies and movement power-ups.
Invincibility
First enter ENCHILADA as your name to unlock everything. Then go to the character select screen and enter CODY as a name.