Update from last time.. We have downed him now in 10 and 25 man.. Its getting easier and we only use 2 healers in 10 man. Good setup is if you have a good group is to have 2 really good geared healers with at least 500 mp5 while casting. One should focus on the tank while the other do group heals (so bring a group healing class) Me and my paladin healer are very good healers with over 2k spellpower and as i said 500 mp5 while casting. A good thing is also to bring a druid, either feral or balance to restore mana on the group healing class. PS: Dont bring any dps under 2000 or you will fail. Most should be good geared, 1 or two can be undergeared for this fight but i dont recommend more.
Basicly when we start the fight, we ask that all melee come to the group healer while blizzard is on his foot to lessen the dmg done on the melee. And we mark off the healer so when he/she moves its important the ranged move with her/him. A few good tips for priest healers is to use POM alot. I casted it on every cooldown. i also used COH alot. POH is not recommenable since the casting time is too long. Frost resist is not nessecary for this fight at all, however good gear is
Reason why hes so hard for some is that the last boss is easy. Blizzard done this on purpose.