At the title screen press Up, Down, Left, Right, X, Circle.
All Robots in Versus Mode
Enable the All Robots in Story Mode code, then return to the title screen and press Up, Down, Left, Right, Up, Down, Left, Right, Up, Down, Left, Right, X, Circle.
Level Skip
"All Robots in Story Mode" code must be done first prior to performing this cheat. Pressing L2 anytime in Story Mode will instantly jump you to the next level, your score will reset to zero however.