Creepers

Creepers is a 1-player arcade game for the VIC-20.

The player controls a ship that moves vertically along the left hand side of the screen and fires to the right. Aliens try to transfer blocks from the bottom to the top of the screen. Each alien travels in a vertical path, and if an alien does not find any blocks, it turns into a deadly mutant that streaks towards the player. The goal is to shoot all aliens before they can fill their stores. If this happens, the player loses a life. Every harder level, more aliens move at the same time.