Your almost right Mengala, My guild just completed this three times tonight. The priest is non agro and non targettable, after clearing the room of spawns, one person walks out over a bridge type structure that goes out into the next room up a small flight of steps.
The person walks out onto it gets rooted with the message ' A gostly shackle binds your ankles'.
The Grimling priest then calls for his master to rid the temple of intruders, and the first waves of skeletons start. AT first they come one at a time about a min apoart, but soon they speed up and after a while they are coming at you from all sides. The person on the bridge remains rooted throughout the entire thing.
Anyone who walks onto th bridge wil also be rooted, so whatever you do, dont follow mobs if you get a runner. Just nuke it to aggro and it will come back.
We discovered that the best person to go onto the bridge is one of the clerics as the whole thing is within healing range so he can continue to heal and look after the group from his rooted spot on the bridge.
After the 4th(? wasnt counting actually) wave the priest shouts that he has failed and attacks, at this point he is now targettable.
He has a HELL of a lot of hp and can complete heal. We got the named priest on the first time, and just a grimling priest the second and third.
Only the named priest drops loot worth anything, the plain grimling hight priest drops junk loot.
He respawns back to his spot, non targettable and non agro Immediatly he is killed.
We did it with 2 groups of 55+ people with the main tank being a lvl 60 pally, with the only death of the whole night being when one of our wizards got lost in Grimling forest on the way there and got zapped by a green con sonic wolf...
Was a hell of a lot of fun.
Oh yes, one last thing, one of our mellee went onto the bridge the first time and got rooted, we decided we could Call of the hero him off the bridge and back to the fight.
When i cast CotH i got the message:
'A ghostly vioce tells you, There are no heroes here. Well ok, maybe just one...'
and a grimling Hero appeared in front of me.
HE was yellow to my lvl 57 and was ready to attack. He was mezzable until we were ready to deal with him, and i was able to malosini him first time. He didnt hit particulaly hard according to our tank, but had a crapload of hitpoints and used a lot of mana up as we burned him doen as fast as we could.
I always thought this was a story until tonight but in acrylia it really happens.
Tired now, need sleep.
Hope that answers all you want to know about this dude and how to take him down.
Be lucky and good night )