Stargate or Defender II may be used, since they are the exact same game.
Two joysticks are required for this one-player game. Use the left controller for manuevering the ship and firing on the aliens. Use the right controller to activate Smartbombs and Inviso, and to jump to Hyperspace. For every 10,000 points, players earn another ship, another Smartbomb, and more Inviso.
Difficulty switches are not used in this title.
Old rules edited 10 Dec 2018 Stargate or Defender II may be used, since it's the EXACT same game.