Resilience Will Fix It

I've been wanting to bring a warrior tank for this fight actually, for once Intervene has the potential to save a lot of lives. Unfortunately we don't have any left...

For this achievement, a warrior tank isn't even necessary. Intervene helps, but not as much as you'd think. If you have a warlock, curse of weakness is actually really strong, though spread out here honestly is the biggest favor you can do for your raid. We just took advantage of the fact that when an NPC drops his aggro and goes after someone else, if they're far enough away, by the time they get to them, they typically have dumped their threat on them and go for someone else across the room again, so they just run around like idiots most of the time as we burn them. I was on the resto druid full time, so I didn't see too much.

I just know our warrior didn't really do anything at all other than charge/tank the rogue.

Well, if you have a warrior tank you don't need CoW. He can just demo shout every once in a while. It's no good for Heroic, but it'd do for the achievement.

Spreading out is definitely a good idea.