Zub

There are ten planets in the Zub system, each of which is connected to some others by a system of teleports. You start on planet 1 and must get to planet 10 and back. There are platforms on each screen; when you stand on one you can move it by crouching and pushing left or right. Use the platforms to get up to the three teleports at the top, your destination depending on which you choose. There is always one alien on screen at any one time, which descends from the top and attempts to knock you off the platforms.