You have uncovered the secret of the Circle of Thorns mages, that they are ancient spirits who inhabit the stolen bodies of their victims.
How to Get
Defeat 200 Circle of Thorns mages.
For Heroes, this badge can easily be earned in the southern half of The Hollows where groups of Circle of Thorns litter the area. This is easier to do at a higher level where one can just run around defeating mages and ignoring the other minor enemies.