I do not like polymorth. (well, it can be good but I can think of better skill trees).
You already have the mask to turn into another race (at least I guess so) and for elementals, animals, skelletons and some other things you already have summons.
@magnifico: Sounds nice, but I do not think you can turn yourself or others into a cloud or a pool of something. It is already hard to animate "normal" creatures. How should a cloud or pool or a man with tentacles move, attack, cast spells or react to an attack? And how do you visualize it in a way that it looks not totally silly? Well, if you have answers to these questions (I have not) than it might be good.
Prof. Dr. Dr. Mad S. Tist
World leading expert of artificial stupidity.
Because there are too many people who work on artificial intelligence already