It's the pet of Dremcis Fuiloltair, you probably(if you are for exapmle a ench+druid) have to kill it(and it's 4-5 orange-red slime pets called Fuilslathach) first because it switches aggro and deals high dmg while fighting Dremcis Fuiloltair.
Edited, Aug 1st 2012 11:31am by Hexaglot