Unlock Hard Mode:
Beat Nano Breaker to unlock Hard Mode.

Unlock Splatter Mode:
Beat Nano Breaker to unlock Splatter Mode.

Unlock Keith:
Beat Nano Breaker to unlock Keith as a playable character.
Unlock Mini-Game:
During game play press Up, Up, Down, Down, Left, Right, Left, Right, X, O to unlock a shooter Mini-game.