

Thanks to Calex dEUS who mentioned that if you're running low on Seeker Rifle ammo you can bump the difficulty down to casual and one shot them. There is a save station on the wall as you enter the room before you go down the ramp. If you manage to run out of Stalkers just exit to the main menu and try again. There are plenty of stalkers in the room. If the stalker manages to get away just refill your stasis from the station on the wall and try again.

Once the Stalkers come out wait until one is peeking out from behind the shelves and use stasis on it, once it is in stasis zoom and try to hit the stalker in the head, I played on the survivalist difficulty my first playthrough and it took two shots to the head to kill him with no upgrades. You are in a room with a bunch of orange shelves and there is both a stasis station, and throwable kinesis spears on the ground. I got this one the second time Issac faces a group of stalkers after killing the Tormentor. This achievement is not super easy as Stalkers are really fast and on most difficulties will not die in one shot.

Obviously, for this achievement, you'll need the Seeker Rifle, you'll need to aim (LT) and select the alt-mode (RB) before firing the killing shot. You can pick them off one by one at your leisure by repeating the in-shoot-out pattern. As soon as you shoot once, back up through the doorway, and they will not run at you and attack (or will even turn around if they were already running your way). Simply cross into the warehouse, wait for the Stalkers to run around and take a hidden position, and headshot them a couple of times when they peek out. The doorway from the stairs to the warehouse room is a transition point in the game, and if you cross to the stairs, the Stalkers become disinterested and wander back into the warehouse. As soon as you hear the Stalkers make noise announcing their arrival, run as fast as you can to the stairway you entered from. You enter a warehouse room, where you trigger about 6 or so Stalkers halfway across the room. I found a nice way to kill Stalkers at your leisure in Chapter 6.
