The Web Comic Ava's Demon has had some interesting transformations lately.
The normally meek Ava gave in to the demon, Wrathia, possessing her when faced with potential death and has now started to go on a rampage fitting her demon's name
The art is quite amazing, albeit terrifying as of late (see
http://www.avasdemon.com/pages.php#1288 when the main antagonist's 2nd in command was going to brainwash her into becoming a follower and transformed someone else instead) I suppose it could also be considered an Evil Transformation since it is an evil galactic cult.