Medusa (Age of Empires)

Age of Empires unit only. Looks exactly like a villager, builds and collects resourses like a villager, and can be trained as a villager. When killed, it turns into a Black Rider. When the Black Rider is killed, it turns into a Heavy Catapult. After that is killed, it is gone. Very handy for defending your town or for front line building. You can train as many as you can support.