I was fighting monsters in The Docks when I came across a Tormented Necromancer and promptly gave chase, only to notice it flew off screen and possessed a monster in the process. Fighting ensues.
Since the monsters were somewhat scattered about, I began to use Ice Shot + Chain to deal with them. Upon firing the last arrow for the killing blow... http://i.imgur.com/6WWCwKr.jpg
I have yet to encounter another Tormented Spirit to fully verify this was indeed caused by Ice Shot + Chain or if it was just some freak accident that just happened to have the right timing, but at least this may provide some insight as to what may have caused this.