Enter the following codes at the Extras menu.

Every cheat:
Press Left, Left, Right, Right, Left, Left, Up, Up, Down, Down.

Paintball mode:
Press Right, Left, Right, Left, Down, Down, Up, Up.

Every multiplayer skin:
Press Down, Left, Up, Left, Right, Down, Left, Up.

One life mode:
Beat the game on hard.

Special thanks to Revolution readers Tricky Dick, DaBoss, Salome, and Jordan!