Alien Syndrome for the Sega Game Gear. Although Alien Syndrome is a typical overhead, character based shooter, it's a pretty far stretch from linear games like Commando. Players can take control of outer space commandos Ricky or Mary (who are absolutely in no way related to Michael Biehn or Sigourney Weaver), or both for two player simultaneous action. Each of the seven stages takes place on one of the invaded colonies, where the aliens have trapped the humans in cocoons and biologically contaminated most of the structures.
