Just Can't Get Enough (25 player)

If you're soloing, he will despawn if you don't stand in the middle until he initiates combat. You gotta either kill the aboms quick and stand in the middle or aggro them and lure them to you. You won't get 18 running to you by themselves.

Just did this as a 626 Hunter, but should be achievable by any class with a ranged ability with a short to none cooldown.

Now, the trick with this achievement is that you can't leave the center circle, or else Kel'Thuzad will despawn. But the abominations are all around the edge of the room, and not enough of them spawn to come to the center for you to kill to get the required 18.

HOWEVER, I found that at the edge of the circle, someone can target the abominations in the back with a ranged ability, which will aggro all three of them. I 'm not entirely sure if this is possible for everyone, but at least it is for hunters.

I just put my pet onto passive (to ensure I got credit for the kill instead of my pet, who obviously does not have achievements.), and went around and targeted each set of three abominations. I'm sure I killed more than the required 18, but there's no marker to alert you when you've killed enough, so I recommend just killing them until Kel'Thuzad despawns them and becomes attackable. Then kill Kel'Thuzad as you normally would, and the achievement will pop when he dies.

Happy Achievement Hunting!

Obvious Depeche Mode reference is obvious