Translated from the popular arcade game of the same name (sometimes also known as Stargate), Defender II for your Atari 2600 provides the same play mechanics as its arcade ancestor.
Players pilot a small key-shaped ship in a side-scrolling environment with the goal of destroying each and every alien enemy on the screen while protecting the humans. The plethora of enemies you face in Defender II are Landers, Mutants, Yllabian Space Guppies, Firebombers, Pods, Swarmers, Dynamos, Baiters, Phreds and Munchies.
Alien Landers are kidnapping humans with the intention of turning them into mutants. You must destroy all Landers that are carrying humans and catch them before they fall to their death. You start the game with three ships, three smart bombs, energy for hyperspace teleportation and six seconds of Inviso -- your cloaking device.
Use the Stellar Gateway to warp you to humans who are in danger. If all humans are safe, the Gateway will transport you to the opposite side of the planet. Enter a Gateway while carrying four humans, and you will warp ahead three levels.
Points are awarded for enemies destroyed, as well as for the number of humans left at the end of each level.