Champion costumes:
Beat the game in championship mode to unlock the champion costumes.
Fat boxer:
Press Right, Right, Up, Down, Right, R1, R1, R2 at the character selection screen.
Huge gloves:
Press Left, Right, Up, Down, R1, R2 at the character selection screen.
Skinny boxer:
Press Right, Right, Up, Down, Right, R1, R2 at the character selection screen.
Zombie boxer:
Press Left, Up, Right, Down, R1, R1, R2 at the character selection screen.
