[thejeff]

But against mistform that shouldn't work.

It's broken by magic or lots of damage, right? I'm not sure how "lots of damage" is determined.

Arrows and slings would just do 1 point. I don't know about poison. It shouldn't be affected by the mistform, but I don't know if it would break it.
Flaming arrows would break it. F9 bless (or D9?) will break it.
Trampling?