Ok I have been camping this guy for days in the little room on the basement/pit floor, or what ever you call the lover lvl of this zone, all the way up in the most northern room on that floor. This room is off of the large room with the lava "river" thing in it that has all the different indefferent con races working the forges. There is a little room in there that has 2 see invis guards on either side of the door to that room. The litte room itself has a forge in the back right hand corner and a quest Ogre before the forge on the right and a see invis mob in the back left corner. Ok now all should know where this guy is.
I had assumed that the see invis mob in this little room was the PH and that this Tagrin fellow should pop or the PH would pop again after the death. Boy that is so not how this mob works. Then I guessed that he must be like Glykus on the other end of the zone, 24 hour spawn, yea that is not it either. After sepending close to 8 days in this zone during fables trying to get him to spawn I have nothing except he is a random timed spawn in the little room in the back-middle. I have killed most named in the zone during this time and have then gone to check to see if that was the trigger and I could not confirm antyhing. The only thing that was close was that on the 7th day I killed the oversear for the first time and then the next day Tagrin was spawned. Other than that you just have to keep checking to see if he is up, and yea you cant track him from the zone, need to be close.
He is not that hard hitting of a mob and I resisted all of his ae but he has friends. If you do not kill all the KoS mobs in the room next to him they will all rush in and start beating on you healer. Also, at about 85% or so he starts poping pets, similar to the warrior weapon pets but they look like splitblades of destruction, and they also go right for the healer and by the end of the fight I think I had about 8 or so up. They do not despawn when he dies either. Died 5 times trying to kill him with a 80 ranger + cleric merc and a 76 shaman + tank merc and the lowest I got him was to about 45% before adds killed healer merc and shaman. Called in a great 85 druid and fantastic 80 cleric guild member and the fight was then trivial. Good luck on the mask, I got mine and was hopeing to get one for my druid but it is just a crazy unpredictable camp.