Pfft, excellent. Uh, speaking of which... Say, theoretically, a character is enough of an jerk that they don't particularly care to out themselves as a non-human and would just leave the poor person they switches powers with to flounder. How badly would that affect the world regaining its balance?
Also: Pick and choose from that laundry list. I can dig up links that better illustrate what he can do, if there's anything you're particularly interested in/don't understand. I'd suggest leaving the True Form thing alone, because canonically we don't know what Sebastian's true form looks like.
Oh! He remarks that it's difficult to adjust his strength if he's fighting a human he doesn't want to kill, since humans are so fragile, in case you want to play out the first ten minutes of Disney's Hercules.
Less "powers" aspect of his being would be stuff like: he can sleep but doesn't need to; can eat human food but it doesn't taste good (he had trouble cooking at first because he had no idea if what he made tasted okay) or give him any nutrition; he's very hungry ): and only souls are appetising. If you want to play around with any of that.