Formist (3.5 Base Class, PEACH)

[Baron Corm]

Assuming you're sending humanoids with class levels at the formist, it's very weak until level 5, overpowered at level 10, and way overpowered at level 15. The reason for this is, a PC's CR is equal to his class levels. So you can say that the CR monster you can shift into is the level PC you are effectively. Except that you can also be any other type of PC the situation requires with a standard action.

If you send monsters with crazy abilities, it just depends completely on what you send, and there is no way to comment on balance.