I had beaten the red dragon in Water Gem quest before and was stuck on the Trial of Fire quest. Then just now I got the Sun Priest as the last boss in trial of fire. I won with my Warlord and Warrior dead, and my Hunter at 1 HP. Got an achievement for it too. The fun part about that win was that the Sun Priest was on his way to gank my hunter and end my quest, but the hunter had a Overwatch card so when the Sun Priest moved, my hunter got a shot off.
So I have 2 of 3 quests completed in order to unlock the last class. Anyone know what it is?