To view all levels, enter the following button presses at the title screen: L, SELECT, A, SELECT, R, A, L, SELECT. Press SELECT and R or L to scroll through the levels. Then press LEFT to make the boomerang apear around the word "Start."

In order to continue forever, use up all of your lives in the first level, then tap B B B when the continue screen comes up. The counter will stop counting down and you'll be able to continue forever.

Enter this code at the main title screen, to unlock cheat mode: L, SELECT, A, SELECT, R, A, L, SELECT.

Unlock cheat mode, then start playing the level of your choice. During gameplay, hold SELECT and press B to get 99 of each weapon.

Unlock cheat mode, then start the level of your choice. Hold SELECT and press the D-Pad in any directly to move freely. Weird!