Killed this last night on live.
Adding to MysticPandas guide:
Easily doable with a normal 8-man setup: 2 tanks, 2 healers & 4 dps. Just need 1 ranged dps for the Rancor add. The adds spawned opposite the boss, on the shore, once boss is at 90%.
The Primal Destroyer - Have your best tank on the main boss.
Drooling Grubling - The rancor chain casts acid spit, which leaves ooze on the ground (can't see it since you're balls deep in the water :P). Have your assigned ranged dps take aggro on this guy and keep on moving. He casts his spit so often, that you really have no time to stand still to cast anything. Once the ranged has aggro on the rancor, he can dps the boss with instants. If the ranged keeps on moving, he wont take any dmg, as the spits dont do dmg on hit. Only the ooze on the ground hurts.
Primal & Unnatural Grubling - These 2 do so minimal dmg combined that 1 tank is enough. Just have the offtank tank them away from the group cause of Primal Grublings aoe aura.
Dropped 2x 22 Barrels.
Killed Him today in beta 12/4. Less than ideal group consisting of 2 Melee Tanks, 1 Ranged OT, 4 Healers and 3 Dps but we got it done. He has a relatively short respawn timer. Less than 6 hours. He dropped 4 Artifact (Purple) quality items 46+.
Phase 1 - Tank and Spank until 90% in Flashpoint gear it is not possible to solo heal a tank. Requires two Healers. Easiest to tank him where he stands. He has no special abilities.
Phase 2 - Three adds spawn all level 50 elites. All three have a Buff called Favored of the Primal Destroyer. That states if the adds are killed the Primordial Destroyer will enrage causing a wipe. Simply have tanks pick up their targets and hold until the Primal Destroyer falls. He only had 485k health he fell rather quickly. Afterwards the adds do not disappear so simply kill them and collect your loot.
Drooling Grubling - is the Rancor looking one. He can only be tanked by a ranged tank. He can be off tanked by a DPS cause he doesn't hit that hard but the off tank requires a dedicated healer.
Primal Grubling This add looks almost identical to the boss. Does a fair amount of damage and radiates a AoE dot like effect that deals damage to all nearby players. Tank away from the group.
Unnatural Grubling This is the blue monstrosity. He puts a stacking armor reducing debuff on the tank. While it was not necessary for our group to switch tanks on him I would suggest it in an organized group. He starts to hit very hard as the fight goes on.
Happy Hunting.