We are curently debating about unraveling on a french forum, and not able to agree each other.
I think this definition applies to all effects, including hedge powers and might, so it's applicaple to the spell "eternal oblivion" to destroy the might of a creature
Other think this definition is only available for Spells, to destroy a spell wich has just been casted, and not for destroy might
You might get your answer by reading the paragraph you quoted above completely:
(underscore mine, as usual). As a Pralixian Mastery listed immediately below spells to destroy or control non-Hermetic magic, it is not restricted to boost spells weakening or destroying Hermetic spells - but it is restricted to boost spells weakening or destroying spells.
Unraveling mastery is targeted specifically at PeVi spells that affect spells and powers, whether they are Hermetic or not. This is part of the focus of the Lineage of Pralix. It does not affect all PeVi spells; it cannot be applied to a Might-stripping spell like Demon's Eternal Oblivion. The full description makes this clear; it destroys a targeted spell, not a Might score.
The Apotropaic mastery found in RoP:tI can be used for destroying demons; it's also pretty good for controlling them.
I've never found these effects to be in any way unclear. It seems completely transparent that Unravelling mastery affects PeVi spells intended to destroy other spells and powers, be they Hermetic, hedge magic, creature supernatural powers, or even supernatural abilities. An example spell from HoH:Soc in the Line of Pralix section states that a Shapeshifting ability counts as ability scorex5 for effective level to dispell.
Now, these guidelines state need to be familiar with the kind of magic (or "power") you Unravel, and that you need to specify. Examples are Hermetic Terram magic of shamanistic spirit magic. This makes Unravelling the Fabric of [Form] much more efficient that the more general Winds of Mundane Silence.
However,following this is where things get unclear and contradictory. What is 'familiarity'? If you've studied the specific power for Insight you are surely familiar, but less ought to do it as well. Is it enough to have observed effects by mundane eyes? Must you use magic? Is the Pralician Comprehend Magic useful more or less the only, best bet? I hope not.
Also, in GotF Philipus Niger has some spells as examples of this, however his are much broader that I'd like. He can Unravel 'Witch Magic' wit no further details given. IMHO this needs specify which Witch tradition (e.g Pomeranian Witches) and also for specific powers (e.g shapeshifting or cursing)
You know nothing Christian Andersen.
It's a well known fact north of the wall that Philipus Niger is not bound by the laws of magic and can dictate is own set of magic theories as long as it make him more badass.
More seriously Philipus Niger is a mess T_T, for his spells ans his focus mainly.
We had that debate ourselves (because it is a mess and we had dozens of non hermetics in our last saga). We ended up applying familiarity if 1) you had at least a level 1 in the MT of the tradition (that would grant familiarity with all their powers) or had studied a tradition for a season in the lab. A little bit more restrictive, perhaps, but much easier to implement in a practical basis.
Yes, yes, people are so clever north of the wall, and completely different rules apply (if any)
But don't tell Philipus Niger he is a mess, especially not in a loud tone!
We recently ended a Rhine saga that did not run as inteded. The Flambeau character has Philipus Niger as Pater, and also TOrmenting Master Flaw.
In our previous Rhine saga I played a magical investigator, and the guidelines you mention fits nicely with what we did. We also allowed that if I used Comprehend magic to observe a given power/type pf hedge magic (e.g cursing) for the three rounds normally needed to use the advantages of Comprehend Magic I was sufficiently familiar to Spont an Unravelling spell for this. But for actually inventing such a spell, or for knowledge of the observed tradition's other powers I needed to do as Xavi mentioned above. It worked well for me. i mean, you had to make an effort for it which serves to support such a character concept and not undermine it if it was made too easy for any other magi with casual observance to do it as well.
I was sorry to see the end of this saga, as I had just started to scratch the surface with this character concept. However the saga was clearly not going as intended, the new people we were taking in deserved a fresh start rather than suffer our baggage of poorly managed ideas. Plus we remembered another short saga where we actually had much more fun than ever before, and we tried to recreate this situation.