Alien Invaders Plus

It's you versus the robotic armada of the Merciless Monstroth, a one-eyed tentacled entity bent on conquest. Use your laser base to take out the enemy cannons and the robots, being careful that you shoot them when their barriers don't block you and when they're not shooting at you! Get shot and you lose your laser base, but as long as you have barriers, you can run under one of them and convert it...