So, after playing the many wave assaults and different modifiers you can do on each level of Arena Difficulty, what is the HARDEST boss you fought in the PRISON of ELDERS?
Mine is Urrox the Flame Prince. Not only is there a massive MASSIVE horde of Thralls and other Hive flooding the room, you HAVE HAVE to stay airborne while his rage is on or each second you're on the floor (he burns the entire floor in an AOE for 9 seconds) ticks for like 25% of your max shield and life. So if you stay airborne is keeps this debuff from hitting you.
The problem? The hordes of Hive don't want you just "flying around" so they shoot you down. Like SKEET son. Pow pow.
But he was probably the most challenging for my team. What is yours?