Dead space-The hunter.
Yes, I know most people here think dead space and every game like it has enemies that aren't any trouble because you can just fill them with bullets, but what about enemies that keep coming, through hails of plasma, fire, saw blades, and cryogenic freezing processes? Thats the hunter. You ca dismember it all you like, but it will grow it's limbs back and continue it's pursuit just too fast for your liking. You'll try to escape it by getting out of the room it's currently in, but soon you'll find it has an all too remarkable knowledge of spaceship vent systems, as it crashes through the nearest vent, looking for blood. Your only choice is to keep running until you loose it, or you find a way to eventually get rid of it.