U.F.O.

This UFO is not your ordinary UFO.

This boss is spawned when you smash the vehicle spawner the Aliened buggy drops and has killed all Space Bosses. He then comes in and shoots you to death. He has infinite health and instant death so you have to get inside the U.F.O. some how and defeat the army of people that are controlling it. He drops a pet alien and a gun (random Expert Mode type)