1) It was official server
2) it was a bug, in which any class with a pet (even frost mages) could go to Mgt and in the 2nd boss (the arcane void guy), he would stack a debuff that increased damage done and size at the cost of increased arcane damage taken.
The catch? The catch (or bug) was that if you manually dismissed your pet (in this case Felguard) he would retain the debuff stacks even if the master left Mgt, and upon summoning that pet again, he'd spawn with the remaining duration of it.