WoWDB

This achievement requires everyone to successfully dance the Devastating Combo and use the special Opportunistic Strike, including both tanks.  Everyone has to dance together and use their special on the same boss; you cannot split it up throughout the fight.  

You can either stack both bosses and eat the failures from one while successfully dodging the other, or you can move the bosses as close together as possible, have the second tank dance separately, but then Leap of Faith him over to use his Opportunistic Strike on the same boss as everyone else.  Remember, there is only a 3 second window to use Opportunistic Strike so this can be extremely difficult to pull off on the timing.

After all that, you must successfully kill the boss to get credit.  The entire raid simply executing the dance will not count and I have heard mixed things about whether deaths will fail this achievement so you might want to wipe it if anyone dies to be safe.  You also must have a full raid; trying to cheese it by bringing less people will not work.

Use Swiftness Potions and any abilities you have like Sprint or Stampeding Roar.  I do not recommend Aspect of the Pack, as if you are clipped by the second boss' attacks, you will be dazed and unable to dodge the intended boss.  Practice in LFR on prior weeks or give raiders who don't normally dance the opportunity to practice so everyone is good at it.

Obviously it is much easier to complete on 10 man by virtue of having 15 less people to mess up.

This achievement is required for the Glory of the Pandaria Raider Tier 14 meta.