Use a Line Gun (the Disc Launcher thing) and aim for the middle tentacle of a Lurker (the little Necromorph that shoots 3 projectiles at once at you). I didnt have mine upgraded when I got this achievement so its possible to get this when first purchase it.
The guy in the video was smart for freezing it with Stasis and moving to its side to kill it but you could also kill but standing directly in front of it. But I would do what he did and freeze then kill the Lurker.
Remember: Use a Line Gun and aim for the tentacles!