Alternate costumes:
At the title screen, enter Left, Right, Right, Up, Down, Left.
Faster running:
At the title screen, enter Left, Right, Up, Down, Down, Right.
Infinite energy:
At the title screen, enter Up, Up, Left, Down, Left, Right.
Power-up attacks:
At the title screen, enter Left, Left, Left, Up, Down, Right, Left.