Suppose you have a Perdo Vim spell that can dispel Hermetic Animal magic of level 30 + stress die or lower.
Can it dispel Cloak of Black Feathers?
It has been brought to my attention that the RAW do not seem to be explicit about this, so I want to see how people read it. Replies with justifications, or references to places that are explicit, welcome.
I voted "No", since the targeted spell is a Corpus spell (with an Animal requisit), so my understanding is that it must be a Perdo Vim tailored to Corpus spell.
I also believe that would it be Unravelling the Fabric of Corpus, PeVi 20 should be enough since it can dispel effect of 20 + 10 + stress die - but I had to look for the rules since the formula are not intuitive.
It is indeed unclear in ArM5 p.160 box Perdo Vim Guidelines:
A specific type could be Hermetic Terram magic, or Shamanic spirit control magic.
It is not well defined, whether here the Form of the Hermetic magic is solely defined by a spell's primary Form, or whether a requisite makes a spell Hermetic magic of the requisite's Form as well. It looks like the phrase is easily corrected in either direction, though.
Making spells with requisites easier to dispel just appeals to me: using several Forms in a spell renders it vulnerable to several ways of dispelling it. So I vote yes.
Cloak of Black Feathers is not an Animal spell, so no.
If presence of a requisite attracted a spell into that requisite's Art, suddenly a lot of abilities and powers that are currently limited to a Form or two would become vastly broader in applicabliity. For example, the already powerful Minor Virtue Mythic (Professional) (see Mythic Farrier, G p.76) would effectively allow creation of enchanted devices of anyy Form, and the Master of Form power from RoP:M p.39 would effectively be broadened to cover Muto and Perdo effects of any Form (at the cost of an extra magnitude to add a requisite).
Also, in terms of game balance, I think that dispelling is already too easy, and spells with requisites already too hard. Making the former easier, and the latter more fragile, exacerbates the problem.
Although Cloak of the Black Feathers is listed under Corpus spells, IMHO it cannot function without the Animal component. If the Animal part of the spell is disrupted, then the whole spell unravels.
So I would tend to say that the spell would be dispelled by Unravelling the Fabric of Animal as well as Unravelling the Fabric of Corpus.
Does the Ringing the Changes insert in the Bjornaer section of HoH:MC offer any insight?
I think that I'm between the opinions of ezzelino and Arthur: if the requisite was necessary - it raised the magnitude of the spell - then Unravelling the requisite Form would disrupt the entire spell. If the requisite was useful but not strictly needed - like adding casting requisites to ReTe Unseen Arm; no increases to magnitude were added to the spell - then Unravelling the requisites would have no effect.
I've flip flopped but I've now come down solidly on requisites are integral parts of the spell and should widen what affects the spell.
To me there are really big problems with spells if you start considering the requisite to change what the spell fundamentally is. Then you open a huge can of worms. For example, does someone use their Magic Resistance against the actual Form or the requisite? If so, do you use the higher or the lower? How about vis? If there are a bunch of requisites, can you dump tons more vis into the spell of many different types? If your lab has Muto +3, Corpus +2, Animal +4, do you add +5, +7, or +9 to your Lab Total for Cloak of Black Feathers? And then there is this stuff about PeVi and MuVi that are limited to certain Forms.
Technically, this spell is a MuCo spell, not an Animal spell at all. Animal only limits how much Corpus you can use. Considering the massive can of worms that opens up when you consider this an Animal spell as well, I am really surprised so many people are voting for it counting as an Animal spell.
You add 3 to your Muto, 2 to your Corpus, 4 to your Animal, and then resolve normally with the lesser of your Co/An. Or take the lower Lab Total of MuCo+5 and MuAn+8. Requisite have always worked that way, no?
But I agree that you cannot dispell requisite, only the main TeFo.
OK, that's definitely non-canonical. Lab bonuses add to the lab total, not to the Arts. That's important for other reasons, too, like not multiplying them with Affinity.
Likewise, that would definitely be non-canonical. Lab bonuses either do or do not add to lab total.
With lab bonuses, no, definitely not. Here is the rule:
Bonuses to Lab Totals from all applicable Specializations are cumulative. The value of an Art Specialization adds to any Lab Total (but not Advancement Total) involving that Art.
So you determine if the effect uses that Art, and then, if so, you add it straight to your lab total. If it applies, it is added. If it doesn't, it is not added. And that's it.
This is explicitly addressed (ArM5 p 115), and you use the primary Form.
That would need to be addressed anyway. Actually, let me create a new poll. Looks as though that has to be a new thread, as well.
So, you agree that an Animal Specialization adds to Lab Totals to invent Cloak of Black Feathers, then? Animal is certainly involved in the Lab Total. (The rule says "involving", not "using", if it makes a difference.) It may well be supplying the Form score.
This may well need a clarification whatever the decision.
The dispute could well be described as being over whether this statement is true. The spell turns you into an animal. It is definitely using Animal power. If requisites really were just passive limitations on how much of the primary Arts you could use, this would be a lot easier. However, they are not — they incorporate some of the magic of that Art into the spell.
The fact that the original poll is exactly 50/50 suggests that a clarification would be a very good idea. I'll see if the vis poll suggests a particular solution.
Since the game has been going for decades without anyone noticing that this is unclear, but with a 50/50 split in the belief about what it clearly says, strongly suggests that either solution works perfectly well. I do, however, feel that this is fundamental enough to make it worth clarity in the rules.
Ok, so it means you'll want to add free requisite to better Arts, as this will give you free Lab Total bonuses. That makes the universe more hermetic. XD
Yup, that would be an ugly consequence.
I couldn't quote for you an explicit statement, but this is true by an implicit statement.
The Technique and Form are listed in the heading the spell is found under. (p.115)
We can note the singular for Technique and Form and then we can look at p.131 to see that Cloak of Black Feathers truly is a MuCo spell, not an Animal spell.
Certainly. That's why this thread came about. 
And it wouldn't be bad to address some other things I noted. As Tugdual pointed out explicitly and I implied earlier, there are a bunch of abuses that can be opened up, like adding a requisite that theoretically should make things harder but might just get thrown in to abuse a rule exploit.
I'm tempted to say something like
"Hermetic magic is at its strongest with one Technique and one Form used; Art requisites are always a complication that weaken the structure of the magic. Effects that would strengthen a spell can never take advantage of its Art requisites and are always hindered by them; lab totals never increase because of Art requisites; requisite Arts never allow the use of vis that does not match the spell's basic Technique and Form; blah blah blah. Effects that would weaken a spell can always exploit an Art requisite and are never hindered by them, yadda yadda."
Now, I'm sure, especially in that incomplete form, that sort of principle is just begging to cause the sorts of messes that are famous from discussions of magic resistance. And with my flu-fogged brain, I'm certainly in no shape to evaluate them, much less anticipate and respond in advance. But, so caveated, that's what I currently feel.
The polls continue to be almost exactly evenly split, on both threads.
I think I will go with something along the lines of "Requisites do not count as the Arts of the spell for any purpose beyond the calculation of the Casting Total or Lab Total". (So, the "No" answer to both polls.) I can see problems with that, but the potential problems with alternative solutions look bigger. (I like @SEE 's suggestion, but making it clear does not look straightforward.)
There is still time to make a determined effort to change my mind, however.
A possible abusive scenario with this proposal of yours:
I know that a Magus has Flawed Parma Magica (Corpus) and is a Mentem specialist.
I want to learn his secrets. But I doubt I could overvome his Mentem Resistance. So I create a In(Re)Co(Me) effect that forces him to speak his secrets out loud.
I now have used requisites to subvert his Magical Resistance.
Would this be an unintended way to go about it?
Otherwise you may want to add "Magical Resistances" to the list of things Requisites affect.
It has always been explicit that Magic Resistance is based on the primary Arts, so this has always worked. It's a violation of the Code, requires extensive research, and involves a specially created spell. This isn't abuse, this is a story seed.
I missed the boat on the poll.
I'd have noted "no" though.
Consider this: Many Muto spells - all Shapesifting for instance - use two forms. Lots of Muto stays within one form, but all the rest?
Should Shapeshifting or similar dual-Form Muto spells be a) harder to dispell than other spells, b) easier or c) the same?
I say "the same", so I'd rule an Unravelling the Fabric of Corpus can nullify a Shape of the Woodland Prowler just as well as Endurance of the Berserkers.
And if I cast Unravelling the Fabric of Animal on twio wolves, one may revert to beign a cat again, but the shapehifted human is unaffected.
well, if you create a spell that forcefully move his jaw and make his vocal chord utter sounds, yeah, that's a ReCo spell. But if you want to force him to talk, your primary art is going to be Mentem, no matter how you tweak the spell.