It seems the aliens didn't get enough punishment the last time, and now they are determined to take out the humanoids that survived the first invasion. Taking no chances, they're bringing reinforcements. But then, so are the humanoids: the fleet of ships known as Defenders have returned. Not only do the Defenders have all the original tricks at their disposal, they have some new tools as well. Most important is the Stargate, a portal that can warp a Defender out of danger, or into the perfect spot to rescue a humanoid in peril!
Once again, the main enemy is the Lander. Landers appear in packs, scouring the ground for humanoids they can kidnap, whisk off into space, and turn into Mutants. As much as possible, you must destroy the Landers before they can grab any humanoids. Humanoids cry out when a Lander succeeds in capturing one. When that cry is heard, a Defender must find and destroy the kidnapping Lander before it can disappear up into space, then grab the falling humanoid before it crashes back to the ground. Humanoids can survive short falls, but long falls are deadly, and so are the Defender's laser shots!
Humanoids pulled into space are turned into evil Mutants. When that happens, the only thing left to do is destroy them before they destroy you, and then protect the humanoids still left on the ground. If all humanoids are turned into Mutants, the entire landscape is destroyed, leaving you in space and battling for your life against swarms of Mutants! Every five levels the Defenders are assigned a new group of humanoids to protect, so if all current humanoids are lost, the Defenders must face armies of Mutants until after the next fifth level.
Several other alien types help defend the Landers in their quest. Bombers wander up and down the sky, leaving floating mines in their wake. Pods seem harmless enough as they float over the countryside, but they unleash small, pesky Swarmers when shot. Yllabian Space Guppies shimmy their way through space, alone or in packs. Dynamos swoop in, firing Space Hums at the Defenders. Firebombers are even more agressive, spewing dangerous Fireballs. And if a Defender dawdles for too long, new enemies appear, including saucer-shaped Baiters, and hungry-looking Munchies, Phreds and Big Reds. These new enemies slice through the air, homing in to distract the Defender, or worse!
The Defender's laser cannon is the primary weapon against the aliens, but Defenders also have Smart Bombs, Hyperspace and Inviso at their disposal. A Smart Bomb will instantly wipe out every alien visible on screen. Humanoids will survive, even ones in the air, but then they will still have to contend with gravity. Smart Bombs are great for getting out of tight jams or rescuing several kidnapped humans at once, but there is only a limited supply, so they must be used carefully. New to Stargate is Inviso, which renders the Defender invisible and invulnerable to aliens, for two seconds at a time. Inviso also must be rationed for most effective use. A new Smart Bomb and extra Inviso are awarded whenever enough points are scored for an extra life. Hyperspace allows the Defender to jump to a random location. Because it is random, and also because a Defender may not always survive a jump, Hyperspace should only be used as a last resort! More reliable is the Stargate, available on every level. Normally a jump through the Stargate will send a Defender to the opposite side of the landscape. However, if a humanoid is being kidnapped, the Stargate can be used to jump directly to the humanoid's location for a quick rescue!
Completing a level means killing all Landers, Bombers, Pods, Swarmers, Yllabian Space Guppies, Dynamos and Firebombers, along with any Mutants created during the level. Baiters, Munchies, Phreds and Big Reds can be ignored, though of course they will make it hard to do so. Once all aliens in a level are destroyed, a bonus will be rewarded for any humanoids still breathing.
Some levels are dedicated to specific enemies. Starting in level 5, and in every 10th level following, Yllabian Space Guppies swarm in an Yllabian Dog Fight. Then, starting in level 10 and again in every 10th level following, Firebombers team up in a Firebomber Showdown. In these levels, Defenders don't have to worry about humanoids being kidnapped. They only have to worry about survival!
Other secrets exist, waiting to be found. For example, try making a Defender rescue four humanoids and then fly through the Stargate. Good luck in your quest of defence, survival and discovery!