You kill Yauj and Kri. Kill Vem in a corner and wait till he is at 5%. Stop attacking him and wait till the message says,"Vem gains Vengeance."
There will be some loot(like one) and make up an existing item name for the GM to retrieve. Our guild did this and got extra loot on him.
the exploit here would be killing all 3 of them at once and getting 3x the amount of loot you normally would