I found him in the west most chamber of Nadox. I pulled to the corner south of where he spawned, loc of which is neg 84 by pos 2021. One thing not mentioned here is he Enrages at 10 percent. Oddly though they are undead, since my undead spells cast on them, they did not see me with normal invis up. Good luck all.
These are the toughest not named mobs I've encountered in nadox yet. They are located behind the luggald area and seem to drop the coral ring much more often then the rest of the undead trolls.