Hillbilly Doomsday (EP)

The Aliens are the sixth and final boss of the game. Very simple indeed. A UFO will drop down the little green goo enemies you have been killing for a while. As well as those, it will send down some larger, purple aliens. Killing these will take down the UFO's life bar. Just keep killing them until it's dead. If you start this fight with all three hearts, you can literally just stand and shoot, and you will survive the encounter.