Invincibility
On the Pause screen, hold L + R + B and press Down, now your energy will refill continuously.
Level Skip
During game play, hold L + R + A and press Up to complete the current level.
Unlock Mina and Drew
On the character select screen, hold L + R + B and press RIGHT.
Exit Level
On the pause screen, you can return to the level-select screen by pressing L + R + A.