I don't know if anyone else is having trouble with this. I will be starting a FC game soon, and one of my players was a psion in the previous adventure, an "egoist" to be precise. He did rely on a spell in particular, of course: polymorph. I can imagine this spell was "omitted" in FC because of its highly unbalanced nature. Though, it was one of the most fun spells of the OGL. I took a look at the Pathfinder alternative: I don't like it. It's not what I'm looking for. So, can anyone help me with this?
I was thinking of limitations based on XP value of the mimicked monster, but I was wondering what value would be balanced or not for, say, a 4th or 5th level spell. And there are plenty of other considerations, including size, number of "known" or "available" forms, types, Disguise, etc. What would you do?