Unlock All Levels
Start a game, save it, and exit. Now return to the Main Menu and select Resume Game. Highlight your saved game and press Up, Down, Down, Up Left, Up, Right, Down. You sould automatically be brough to the Level Select screen, which should have all levels on every ladder available to you.

Fatboy Mutator
From the Title screen, enter Circle (x3), Up, Down, Down, Up, Circle (x3) to unlock the Fatboy mutator in Multiplayer Mode. This Mutator will make it so that a player gets fatter and fatter as they rack Up frags, and skinnier and skinnier as they are fragged.

Four Players Without A MultiTap
For this you need a USB keyboard and mouse. You can also play using two keyboards and two controllers by setting the controller configurations so the keyboards and mice are in the third and fourth player positions.

Regain health
Pause during a game and press Down (x3), Left, Up, Right.

Level Advance
Pause during a game and press Up, Down, Left, Right, Right, Left, Circle.

Cheats