We have done this achievement twice now, once before the patch and once after the patch ( 3.0.8 ) and both times we did not get the achievement.
Our group setup was:
DK (OT)
Warrior (MT)
2x Mages
Resto Druid
The DK tanked the boss until he got impaled and then the warrior took over. We didn't follow the strategy where everyone moves out of range except the MT but we all stayed in. One of the mages got impaled first. When the boss charged that mage, he died. I guess he was standing too far away (if that matters).
We combat ressed the mage and he got impaled again. After we were all impaled (took us a while to get the MT impaled), we nuked him down but we didn't receive the achievement.
Could this be because the mage died? Could the death bug the achievement somehow?
Note that we waited for the mage to get impaled again after the was ressed.
i suggest you go engage boss with MT, OT and healer, the dps staying away and out of combat until the two tanks or all of them gets impaled. Though, you can arrange the one to get impaled, its still a bit random due to boss charging. This tactic worked for us and was a lot more failproof.
4 of us got impaled, so we stopped dps for like 5 minutes, just to wait for the mage to get impaled. Then finally it happened, we killed him and guess what? No achievement ???
Did this a week or so ago. Rogue, priest, pally, dk, shaman. DPSed him down till he transformed then just stood around while he impaled people. When we all got impaled we killed him and got it. Don't let people die I guess.