Well, if the case is that it hits all players, try to burn him down to 10-5% and then have EVERYONE (excluding one tank that had just reset his overcharged stacks) off the inner platform and then kill him on the outside.
I mean, there is not much you can do if he is hitting everyone for so much, all you can control is not having Overcharged stacks and using AoE raid CD's to help stop the damage.
Devotion Aura, Power Word: Barrier, Tranq, AMZ, etc. just try to negate the damage as much as possible.
IMO it was suppose to only be proximity damage, but it seems like it is either a bug or the damage is too over tuned.
Edited by krazyito65, 05 October 2012 - 12:18 AM.