Beat him my first try at level 12.
As soon as you get a chance, teleport him into your group. My group was able to constantly knock him down, turn him into a chicken, knock down, etc over and over and over again. He never got a chance to do anything else once we got a chance to teleport him and take down some physical armor with a few backstabs and attacks.
He regenerates physical armor so make sure you take it out and he is resistant to physical attacks as well. Just keep his physical armor at 0 so you can continually cast chicken and knockdown effects (earthquake, ram, slam, etc)