Enter any of the following codes at the "Press Start" title screen. Visible confirmation will be given when a code is entered correctly.
Platinum unlock (all boxers, arenas, game modes, etc.): Square, Circle, L2, R2
Additional custom boxer textures (brow styles, tattoos, etc.): L1, R1, X, X, Triangle, X
Big head mode: Square, Circle, Up, Down
Small head mode: Square, Circle, Down, Up
2D/flat mode: Down, Up, Circle, Square
Super mutant mode (characters grow and shrink randomly): Square, Left, Up, Triangle