Shapechanger subtype

[hjs102]

Hello, looking to build a kitsune swashbuckler, but I am confused about their shapechanger subtype. I read that the natural shapeshifting abilities allowed you to get around harmful polymorph effects such as baleful polymorph, but a fellow player said this wouldn't work. He said the second failed save would lower my mental abilities and prevent my shapeshifting. He also said that the only spell this would help me against was baleful polymorph, but only if I failed the first save and made the second.

My questions are:

1. Can the shapechanger subtype remove harmful polymorph effects such as baleful polymorph?

2. What polymorph effects are there that can be removed? (assuming I wanted to keep beneficial effects from allies)

[Drejk]

Baleful polymorph explicitly states that shapechanger can return to normal form with a standard action. Nothing here says that failed Will save prevents returning to your natural form.

I would assume that returning to natural form in this way ends the spell and thus reverses the mental change (the change is part of the spell and has no specific rule saying it lasts after the spell is ended).