In my opinion the polymorpher should *not* be a "spellcaster", there are already too many of those lines.
What it should be is a complimentary skil line. If you *only* go with Polymorpher, you have yourself a controll character. If you pair it with a warrior, essentialy what you get is a chaos warrior from warhammer, if you mix it with a wizard, you get yourself something ackin to the Simic from MTG if that makes sense to people.
The polymorpher should not be another caster, his playstyle should be determined by what you choose to mix his abilities with, as they are highly versatile.
A warrior might use it to boost his stregth, a wizard might use it to warp his enemies, a sneaky type of guy might even use it to create distractions.
