Winter Wolf: yeah, I've thought about it when I was working on it. It isn't its main attack though, but a separate special attack, and in theory Polymorph Self shouldn't grant such abilities. I'll think about it.
The changes you've made to Polymorph Self now makes it worth taking. The things fun, and not overpowered in the least.
I feel greedy. I like the over all spell, but would like to see one or two small changes.
Winter wolf - give it it's breath attack instead of it's claws (possible? legal? to overpowered?)
Mustard Slime - maybe remove it's "Attacks count as +2 weapons" The thing is already awesome. This way, the orge or the Flind has something special about them.
I love both the Flind & Orge shapes. But, I'd give up one of them if the replacement shape has some kind of healing ability or could paralyze (like a carrion crawler or it's souped up version. How cool would that be?)
Mustard Jelly: I don't remember right now why I chose +2 enchantment. I can probably agree with you on this matter, especially because, as you say yourself, this form is really 'awesome' with so many immunities and a powerful ranged attack.
Suggested New forms: I actually thought about implementing a Troll form, but I fear a "cheap" regeneration would be too exploitable, especially considering how much this spell lasts. Regarding a Carrion Crawler form...well, I'm not too fond of such creature and I'm not sure if it can be considered as useful as the other forms, but perhaps it's not required to have equally powerful forms as long as each of it is interesting and doesn't completely outshine the others.
You're right. There's a limit to the amount of text for a spell description, but if it can be done I think I should do it.
On a completely different note, could you add the stats/ resistences/ abilities to the spell description of Polymorph self and or Shapeshift (I think its the lvl 9 spell)? I know you have it here, but it would be much better if I could just look at it in game.