My 10man group tried Bastion of Twilight last night, and we couldn't make any sort of decent progress on Halfus Wyrmbreaker. According to the RL, we have to worst setup of drakes: Slate Dragon and Nether Scion. The tanks were just getting their faces smashed with 40k+ hits, while the raid was taking ~60k damage every 30 or so seconds from the big proto drake. We wiped at least 10 or 15 times because of tanks getting smashed. Another issue is with the stacking -healing debuff that Halfus applies, which pretty much disables the MT until the stacks wear off. Apparently we were going to BoP the MT to remove the stacks and have him taunt it back, but I don't know if that happened or not.
We tried killing Slate first, but that didn't work. Nether Scion first didn't seem to work either. Whelps first didn't work either. According to the guides, when you kill the drakes, it removes the buffs Halfus has...but that didn't seem to happen. Either drake we killed, he kept the +100% attack speed and Malevolent Strikes.
I just don't know what the hell is going wrong that we're doing so horrible on what's supposed to be an "ezmode tank and spank" boss. We couldn't last more than 1 or 2 minutes before one of the tanks died. It's certainly not a gear issue, because we're all in half 346 at the least, with tanks' HP sitting at around 165k. We managed the first 3 bosses in Blackrock Descent without too much trouble, too.
Setup:
Tanks - Warrior / Paladin
Healers - HPriest, Druid, Paladin
DPS - MM Hunter, Arc Mage, Feral Druid, Asn Rogue, DK