Tip for Warlocks, use Angel of Flight. You can last 4 seconds in the air in the cramped left-corner. Mobs are the most dangerous, Urrox himself is only a pain on Arc damage, only because he'll deal tons of damage himself. Mobs however, do swarm on you and do spawn after every Rage. I agree on taking your time, however don't take too long. The mobs will become stronger every wave, to the point where they'll all be Ultras. And Ultra Wizards and Knights will hurt a lot.