Enter the following code at the Options screen....
A - A - B - B - C - C - C - C - B - B - A - A - A - A - B - B - C - C
Pause the game and then enter the following code....
A - B - C - B - A - C - A - B - C - B - A - C
While you're playing the game, press Start to pause, and then press C, A, B, C, B, A, C, A, B, C, B, A, C. If you entered the code correctly, you will hear a tone. The ''Level Completed'' screen will come up and you'll go to the next level, in which you will be invincible.