I was actually thinking I would go with something quite small, for practicality purposes. Even now, I don't think I could force him to remain in any form he truly despised for long - but if he isn't going to be doing any fighting, then the most important thing is that he be easy to keep a handle on.

I could do the easy thing and just make him a lizard. He's already got the tail and scales. The only issue would be wanting to make sure we could keep track of him.