Warpriest Poxxil (click for map image) has a chance to spawn after you complete the third step in the heroic adventure "Disrupting the Ritual" (if the named doesn't spawn, a PH will).
I 3 boxed him today. 97pal with cleric merc, 97 mage with cleric merc, 96ranger with melee dps merc. Has about 7 million HP, hits for 10-12k frequently, and reached almost 7k dps against the pally. It was a 2.5 minute fight with the ranger and mage burning, but the lousy dps merc was on balanced. He conned red at 97, and he dropped the Spellbinder's Scarf.
So this dude spawned in the lv83 version of my mission. Since I thought the dude would be level appropriate like all the other mobs, I engaged with my 3 box crew and 3 mercs.Conned red to me but I thought he would be like lv 85 or something. Anyway managed to get him down to 38% before he wiped us all. Not bad considering he was lv104, lol.