From in-game instructions Try to shoot aliens. There are three types of them : moths, pods & spinners. You score for a moth, 50 for a pod and 100 for a spinner. Pods and spinners fire homing missiles. You score 10 points for shooting an alien shot. Above you there is an acid bath. The bath rots and acid drops fall. These drops will kill you if you are hit by one. If a moth is hot by one, it will mutate to a pod. If a pos is hit, it will mutate to a spinner. Spinners require two hits to kill them. At the righthand side of the screen is a gate. This gate opens with time. If you hit an alien, the gate will open slightly faster. When the gate is fully open, your ship changes into flight mode. You must then fly it through a maze of tunnels to the next level. If you get killed in the tunnels, you go to the next level but do not score a bonus. You get a points bonus at the end of the tunnels. There are nine levels. At level one, the aliens do not mutate and the gate opens slightly faster. After level nine, you return to level one. If all the acid drops out, you die. You have four lives, with a bonus life at 5000 points.