During the second level (The Frozen Tundra) at one point you will come onto a roof with four pods with W.E.N.D.I.G.0 Prototypes in them. At that moment you are chased by a helicopter with Agent Zero (Nord) in it, who will shoot one of those pods releasing the prototypes. Run up to the other three pods and destroy these to release the last few prototypes. When fighting the prototypes take your time, get out of the way on time and only lunge towards them if you're sure they just pounded the ground and won't pull you out of the air. It will probably take some time to defeat all four of them.
If one of the prototypes get taken down by another prototype (it happens), there will be no consequences for the achievement, as long as you fight them all four at the same time and come out as the winner.