Willing Polymorph

[Saeviomagy]

That *troll* or whatever, doesn't lose its extraordinary abilities.. or special abilities..
So it still have regenaration... so if they're trying to avoid it... (too bad for them)

I'm afraid not. From alter self (and never overridden in polymorph):

You keep all extraordinary special attacks and qualities derived from class levels, but you lose any from your normal form that are not derived from class levels.