Say that my Tytalus use MuCo (An) to become a penguin (just an example because i love penguins) for some stupid reason. If I attack another magus or a demon will I have to use penetration to do damage with my natural beak attack or am i considered a mundane penguin? I did not find anything for or against in the ARM5 book in the chapter for parma magica and magic resistance
Say that my Tytalus makesa cr An spell to create a penguin. is that penguin a mundane animal that does not need penetration to attack a demon or is it a magical penguin who cant penetrate the might of the deon, or does the penguin use my penetration to attack?
Because you have a spell affecting you, that spell can be affected by magic resistance and, officially, your vicious penguin peck must penetrate. This can be abused; veteran Ars players call this the "pink dot" problem. Very briefly, a magus could cast a spell creating a pink dot on your sword and now, because the sword has a magical effect, you need to penetrate the magus's Parma. But in the case of using magic to turn into an animal and attack, the rule is working as intended.
The answer to your second question depends. If you are using a Creo Animal spell with a duration like Conc or Sun, then yes, the spell needs to penetrate your target. But if you use a Ritual spell and vis to make the Creo spell Momentary, creating an animal which is permanent, no, that animal does not need to penetrate because it's a natural animal. It doesn't even register as magical.
I agree with Doctorcomics : when affected by a temporary spell of transformation, penetration matters (same answer if creating an animal (or magical animal - I mean a dragon, a vampire... = being with a might) when it's not permanent = you do not use vis under the classical TM).
On the other hand, heartbeast and shapeshifting (and for what it's worth probably skinchanger too) are only magical in the transformation process, not the result. And even for heartbeast, one could ask if the transformation process is really magical considering it is the essential nature, as is flying for a bird, that you can be animal or human, hence it would not be a magical thing, and (if so?) not hindered by aegis and auras. Serf's parma on that one, I do not recall the books answering that question but maybe they do. Someone will correct me if I'm wrong because internet.
It is strange, but this is how it works. You increase your size to gigantic proportion with a MuCo, you cannot squish the puny magus under your feet because it can be magically resisted. However, you can uproot the next nearby tree and swat him like a bug.
The advantage of this approach is that it is relatively simple to understand and those not leave much to interpretation. The drawback is the "Pink dot effect": Mr Parma cast a CrIm with Group target (and a couple of size multipliers), and suddenly not a single weapon of the army nearby can touch him because he casted the spell without Penetration and himself has a Parma of 6 with Imaginem at 20...
I made some House rules around that, but we are entering the area of YSMV and House rules, leave it there.
CrIm wouldn't have this affect, because the weapon is not a magically altered medium: Species have been created, and that's it. Altering the weapon (MuTe or MuHe probably) to be pink, a very easy transformation, would.
The best part of the Pink Dot is that your basic 'sharpen swords' spell cast forcelessly on the enemy makes you immune to them. You can also extend your Parma Magica to your grogs, making your grogs immune to the enhanced swords as well. Designing a spell that actually just sharpens every sword in the fight is pretty effective if you can Parma your grogs.
Oh, then that enemy mage snipes you with Creo Ignem, but that's the life.