Nine extra lives:
Shoot the level 1 exit five times to reach a secret room. Turn around, move down the hallway, and enter the alcove that contains a floating ball. Touch the ball and press B.

Level skip:
Shoot the level 1 exit five times. A total of five exits will now be available that will lead to different levels.

Skip to level 10:
Turn 180 degrees after finding the level 1 exit. Shoot the wall, then shoot the next wall, and touch the glowing section.

Skip to level 20:
Turn 180 degrees after finding the level 10 exit. Shoot the wall and touch the glowing section.

Skip to level 40:
Start at the very easy difficulty. Shoot the level 1 door five times to find a pod with lives. Take the lives, then back up and shoot the pod three times to get a key. It will open a door. Go through it to find more pods. Watch out, as there is a ninja.

Skip to level 71:
Touch the left wall at the start of level 5 five times. Then, shoot the right wall five times.