Lovely art, and a very interesting concept - lots of potential there! It might be interesting if the heroes maintained their position after you possess them, that way you can try and set up interesting moves or maybe even trick a possessed hero into damaging the ghost?
The mage and healer felt a lot worse to control due to a lack of player feedback as to their actions. It would be nice to, for example, see a preview of where the blob/healing circle was going to land before casting it, and a way to know how far along the cooldown timer is.
All in all a great submission though, congrats on getting it done!