These actually have answers though... I'm not sure if this violates essential nature by creoing something and have it lack all the normal properties. Assuming it doesn't...I'm unsure if it would have a perdo requiste or just be a highly unnatural effect and increase level as needed.
I've spent so little time with the divine/infernal books I'm not even sure what part to search in to see if the second question is possible.
I... don't see why not. I'd say a creo effect creates a nearly perfect thing of its kind; you can create lesser versions for free, e.g. rotten meat, but to create things that are unnaturally imperfect, e.g. missing their weight, a perdo requisite does seem appropriate. A very interesting thought.
I too am not very familiar with the Divine and Infernal, but it is my impression that in cannon the answer would be "no". For my games, the pope himself may very well be a diabolist
It is entirely possible, with Creo alone, to create something damaged - but not with its intrinsic characteristics changed, that would indeed require either a Muto or Perdo requisite, depending on what kind of alteration one intended.
Less weight is the loss of a characteristic, not the transformation to something else and is therefore a Perdo requisite indeed.
Quite an interesting idea.
I would have to check on the duration however...
As for the second question, the Divine can never be fooled by the Infernal, that is true. But if it can in your saga... more power to them?
Conceivably, one could create stone that weighed considerably less than a normal rock, because such naturally exists, and is known in period; Verdi covenant would definitely know about pumice, because the covenant is near to Mt. Aetna... There are a whole range of spells that could improve pumice's characteristics (all of them Muto - put them into a constant effect item) - you could make a boat of stone with the stuff.
However, since all things have weight, a weightless object would be considered "Highly Unnatural" and thus, require a Muto requisite to be weightless.
I disagree. Adding a vim requisite does not get around the restriction that only natural things can be permanently created.Also weightlessness is specifically covered in the description of perdo. A muto requisite for weightless stone's unnaturalness is not necessary.
You can create magical creatures by Creo-Animal (Vim), for creatures which cannot be created using "Normal" creo magics.
If I wanted to create a stone, which magically had no weight, I could create one using a Vim req. Same as if I wanted a stone which had some magical property, I would use CreTe(Vi). In this case, the magic is that the stone has no weight.
The difference is that magical creatures do exist naturally in the setting. If weightless rocks exist in your setting naturally then I suppose that creating one with a creo ritual is fine.
However I would susspect that there is no place in mythic Europe that you could to find naturally occuring rocks that have no weight.
You can CrAn(Vi) yourself a real gryphon with a momentary creo ritual beccause int he setting there are actually gryphons, but you can't CrAn(Vi) yourself a real crumple horned snorkack with a momentary creo ritual because in the setting there are no real crumple horned snorkacks (your mythic europe may vary).