Invincibility:
Pause game play and press A(3), B(3), A(3), Start.

Level skip:
Pause game play and press Right, Left, Down, Right, B, Start. To return to the previous level, pause game play and press Right, Left, Down, Right, A, Start.

Reverse D-pad directions:
Pause game play and press Up(2), Down(2), Left, Right, Left, Right, A, B.

Bonus level:
Collect all of the diamonds in level 1. Continue game play to obtain a score that has double zeros in any position (5900, 4005, etc.). Go to the bottom of the level and enter the elevator that travels downward. Do not perform any actions that will remove the double zeros from your score. Run to the right at the bottom of the elevator shaft to access the bonus level.