Quote Originally Posted by Erik Vale View Post
It might make most sense to be restricted based on what creatures you currently have bound [a angel doesn't want to work with a demon, and Deamons are just about universally hated]. pathfinder has [the third party] devil bound creature templates, perhaps some sort of alteration of them would work.

You might also want to figure in some way to fit in the planar binding spells [possibly being able to summon them outside of your own body instead of just in your body].
I like this. It's basically a contract with the entity, and if you're bound to a demon, probably the only other creatures that will put up with you are other demons (maybe 'loths and slaadi). Though if you're a strong enough binder, you might be able to force them to work together. Devils and demons, perhaps. Archons and demons? Probably not, unless you're REALLY good.