I don't know if you already know how this boss works. Anyway I'll explain in few words:
The encounter is split in 2 phases, one of them is the frost one (as the normal one)
In this phase you need to run around the platform and avoid a big ice wall which is trying to catch you.
This wall only appears at the extreme border of the platform, while in the middle (where the boss is), there is no
wall. The normal tactic is to attack the crystals that spawn and to run in the middle of the platform to get dispelled from a debuff
which, once dispelled becomes a frozen trap on the ground.
So it's a bit of a mess. Well here comes the exploit: when you get in the middle of the platform you get debuffed
and you loose 15% of your total health every 1-2 seconds.
If you bubble, become immune or just remove the effect you don't take the damage nor the reapplication of the debuff.
This is quite common on mmoc etc.. But we discovered that if you enter the bubble and use any removal effect of any PVP trinket,
well you get the same result. This is really helpful to healers/ranged, while not that much to melees.
Let me know if this also works for you.
Have fun on heroic Hagara
Edit: sorry for my english but I've been raiding like 12 hour in the past 2 days and I'm at my 3rd redbull tonight
Double Edit: we went back in normal hagara and tryied in 5 people. It even works with the human racial.
A
Apart for humans and pvp trinkets, mage's ice block, rogue's cloak, pally's bubble, DK's abilities etc or any other removal CD, works.
Triple edit: Priest's dispersion, pally's hand of freedom and mage's ice block remove the slow effect but at the end of the CD you start to take damage again.