Zerg is most unique. Only its workers mutate into building. Only its units spawn from larvas. Only its buildings need creep. Only its units and buildings auto regenerate. Only its buildings are alive. Only its supply is a movable air unit that is used for detector and transport too. only it has buildings that can be upgreated to other buildings.
indeed. but the zerg are unquie to play. but they are exaclty the equalitive to the tyranids. minus the fact tyranids are just one big organism, and also that they have psychic powers all of them. and they can own the protoss and the zerg no problem