Ranger needs help

Ok I can't figure out how to beat 'Thorgrim Beastmaster' in the "Stone Summit Beastmasters" quest North of Yak's bend...
Thorgrim Beastmaster is a lvl 28 mob that gets healed everytime I take its life 1/4 down

I have a group of 6 and it is just a stalemate, it can't kill any of my group members but I've been fighting 10 minutes straight and can't beat it..

is there some special tactic I have to use to beat it does anyone know?

HAHA nm finally beat it...I just set my character to attack and left it alone and did other stuff for like 20 minutes and finally killed him