Does Parma protect against Magic Creature physical attack?

Simple question, just to make sure I understand things correctly.

If a creature with magic might attacks a magus with a physical attack -- say, claws and teeth -- the attack needs to penetrate MR, right?
And if so, I use the standard penetration rules on pg. 184, right? [Might score - (5x might points spent on power) + penetration bonus]

It's been about a year since I ran a game, and I'm packing the rules back into my brain.

Thanks!

No, magic resistance does not protect against the claws and bite of a magical creature unless those claws/teeth have been magically enhanced (such as a magical house cat transforming into a lion). This is stated somewhere in canon, but I cannot remember where. It's in some supplement that describes a magical being that can shift into human form. It states that in its normal form its natural weapons are not resisted.

So I assume likewise, a Magi transformed into an alternate form with hermetic magic attacking a magical creature needs to penetrate the creature's MR?
And a Bjornaer does not because it is seen as their essential nature?

The Bjorner Heartbeast, as well as those with the Shapeshifter ability, are considered to be making Instant changes. As such, it's not considered an enchantment, but rather their natural form.

But yes, those under a Muto Corpus (animal) effect will be considered to be under a magical effect, and thus can be stopped by MR or Parma.

Of course, they can also be completely stopped by a ReCo or ReAn "ward against person" or "ward against vicious beast" (I forget which one would affect a transformed human, though). Just not straight-up MR or Parma.

That's all correct. Any other shapeshifting character has no such luck, of course.
EDIT: .... Or maybe I'm just wrong and you should ignore my ramblings.

I just looked it up - it's in the Bjorner section of HoH:MC on shapeshifting, but I THOUGHT it said that those with Shapeshifting are also immune. Serf's Parma, ATM. I do recall the "they're both instant" rule, though.

Heartbeast and Shapeshifter (Major Virtue) transformations last only an instant (though the character retains his new form indefinitely); as such, natural attacks from these "beast" forms are not resisted.

Skinchanger (Minor Virtue) transformations, as well as those produced by Hermetic Muto magic and by typical supernatural creature "powers", are ongoing effects; as such, natural attacks from these "beast" forms are resisted.

Both do, except for heartbeast.

The ward needs to penetrate though.