Revenant

Revenants are mean. I suggest being level 12+ before killing if your playing on hard.

The Black Vials quest Revenants can be found in the following locations according to an unchecked source:

Here's a list of all the Black Vial/Phylactery revenants.

Mage Tower fallen statue                 //confirmed Lower forest ruins                       //confirmed Werewolf Lair                            //confirmed Orzammar palace Carildens cross Denerim (I head it is from a 1 time random encounter, can't confirm. Hope you are a tab addict or you will miss it)