Level Select
At the title screen, simultaneously hold A + C, then press Start. The screen will fade, and there will be a short pause before the game begins. Quickly press B, A, C. The Level Select screen will appear.
Sound Test
At the title screen, press A+B+START, then press RIGHT, RIGHT, DOWN once the game begins.
U. F. O. bonus
To earn points every time the U. F. O. is shot, the first time around during a wave it needs to be hit on the 23rd shot, then on every 15th shot thereafter.
