Shocking! (25 player)

Dr. Egon Spengler: There's something very important I forgot to tell you.
Dr. Peter Venkman: What?
Dr. Egon Spengler: Don't cross the streams.
Dr. Peter Venkman: Why?
Dr. Egon Spengler: It would be bad.
Dr. Peter Venkman: I'm a little fuzzy on the whole "good/bad" thing here. What do you mean, "bad"?
Dr. Egon Spengler: Try to imagine all life as you know it stopping instantaneously and every molecule in your body exploding at the speed of light.
Dr. Ray Stantz: Total protonic reversal!
Dr. Peter Venkman: That's bad. Okay. All right, important safety tip. Thanks, Egon.

At lvl 85 this is quite easy to do, though its probably the most difficult achieve in Naxx 25 simply because people can screw it up. I suggest going with about 6 people as the less there are the easier it is. Split your dps up on each side and kill the minibosses, and keep one healer/ranged dps up on each platform (tank moves thaddius so hes in range of them). Everyone else who goes on Thaddius's platform, in order to get the achieve, you don't have to worry about moving around or anything...all you need to worry about is staying over 10 yds away from everyone else. I suggest typing "/range 15" as a 15 yd preliminary checker to make sure youre far away. Melee dps/tank can spread out on the sides of thaddius hitboxes without being within 10yd and any other healer/ranged dps can stand to the side. Once youre all situated its just a tank-and-spank...we didnt hit enrage with 1 tank, 1 healer, 4 dps. The reason you spread out is so that the positive/negative affect doesnt do any damage to any other players which is the basis of the achieve. In order to know if you've screwed up so that you can wipe and reset the boss if need be, put your Recount onto Friendly Fire, if there's any Friendly Fire you failed that attempt.

today (patch 5.1) i soloed this achievment as blood death knight. tactic pull the 2 minibosses together kill them ,then jump to thadius platform and stay at 1 place for the whole fight,dont move anywhere at all. boss goes enrage after 5 minutes dont worry about it ,didnt use any major cooldowns at enrage, the fight took 15 minutes just simply tank and spank nothing really special, you can try it with uh presence or frost presence if you like it, or equip some dps gear too. i think other classes can solo it easily now as well if you have a bit offheal. you could help your firends too, just tell them die in green pool and you solo it for them.