Astralist Ring of Impulse  

Ok lets see I just went on my vamp after I just respecd, made it to the boss guy killed him he was red to me at 50 my respec is gimp so I dident have enough life after he insta popped or if its a thing you just have to kill more than once but the first guy didnet chase me but the 2nd one did. All the mobs start off yellow then orange and baf and have a huge aggro range. hope this info helps. Try duo him just incase its much easier and faster less your a mauler of course :p