Wow, I seem to just be spamming with achievements lately…  oh well!  Knock, Knock, Knock on wood is the achievement that you get from killing Freya with all three of the elders up, at the same time.  With these elders up party members can get rooted, beams of light spawn that deal damage, and you get silencing ground tremors.  Also, since killing the elders reduces damage different parts of the fight deal, you’ll be taking a lot more damage overall than you are use to with no elders up.  

Resto druids have it good on this fight.  First all, if you get rooted, you can shape shift out.  No waiting around for someone to break you out, or trying to DPS yourself.  Just shift out of tree and back in, and you’re safe!  Second, the ground tremors don’t effect us.  It works more like  counter spell than a silence, in that you have to be casting at the time to be locked out.  With almost all of our heals being instant, just heal though the warnings (using instant casts of course), you won’t get silenced.  As far as the beams of light go, if you have deadly boss mods you can’t not know you’re standing near one, it’s rather loud when it warns you!

The overall damage increase is defiantly noticeable.  I was literally hotting as many of the 25 as I could at all times during this encounter.  Rejuvenation, rejuvenation, rejuvenation, wild growth, repeat.  Pretty much everyone was either taking damage, or would have incoming damage before the duration of the rejuvenation at all points during this fight.  

And of course all the same principals still apply to the fight, kill the trio together, don’t sand by detonating lasers when they are about to die, don’t stand by the green fuming rooted things on the ground, kill the trees, etc.