More power-ups:
Pause the game and press Up, Up, Down, Down, Left, Right, Left, Right, B, A, Start.
Options mode:
Pause the game and press Up, Up, Down, Down, Left, Right, Left, Right, A + B, Start.
Full speed and shields:
Pause the game and press B, B, B, B, B, A, A, A, A, A, Start.
Destroy all on-screen enemies:
Pause the game and press Up, Right, Down, Left, Up, Right, Down, Left, B, A.
Expert mode:
Pause the game and press Up, Select, Down, Select, Left, Select, Right, Select, Select, Select.
