Regardless of whether the spell in MoH is valid or not, a MuTe(An) spell to change metal into (a part of) an animal needs +2 magnitudes to affect metal, rather than just earth as the base 5 covers.
The spell in MoH has "+1 magnitude for equipment" but what does that even mean? It sounds like some attempt to add difficulty in the magic to account for complexity. But why and for what? I think it is unnecessary, because it is not enough to cover changing metal.
And looking at the only other example I can recall:
GotF p96, the talisman of Falke Prima of Bjornaer:
Change Size; MuTe10, Per/Sun/Ind (Base 4, +2 Sun). With 2 uses/day (+1 level), environmental trigger (+3), linked trigger (+3)
The talisman is a silver anklet-ring with crystal and amber.
But the Base 4 MuTe covers "change earth so it is highly unnatural " so the effect lacks the +2 mag for metal/gemstone. Base 4 is also "make something grow up to 8 times its previous volume", this should cover shrinking as well. However it is odd that the guideline mentions "something" rather than "earth" which all other guidelines do. I assumed this required added magnitudes for stone or metal, but 'Object of Increased Size' doesn't! In fact none of the MuTe spells list clearly if there are added magnitudes for stone or metal. Some of them seem to use a Base number already increased, like 'Rock of Viscid Clay'. The way the designs are made is a mess, I'd have preferred if they used a base for earth with clearly indication of added magnitudes for material!
Sorry to run off the rails, but IMHO the spell design is correct with a base for earth and +2 mags for metal. And buth the spell in MoH and Falke's talisman are not designed correct.
Comparing your suggestion for Hibernation flaw with Nocturnal, it results in a worse penalty (-3) but only in the winter, where Nocturnal is-1 and always. For flavour I like the effects with Personality traits. Sadly we don't use Personality traits much in my saga. I mean we play the magi after their personality, we just don't really use the traits for anything.
The lack of "distraction activity" should also count towards giving this a value of Major Flaw.
My initial idea for a Hibernation flaw was to have the magus need to actually hibernate during the winter season, but allow the season to count as Practice, however only in a mental ability. This could be combined with the option of staying awake with heavy penalties, like those above.
Another idea of penalties to represent the character is half asleep might be to reduce lab totals (similar to a minor deficiency). Doesn’t apply to one tenth of the magus art, but applies 25% of the time.
Creative. I like that idea as well.
A lot from this thread inspires me to want to play a Bjornaer magus. But the way my sagas always progress, we have too many things happening to really implement a given magus' house, and it's hard to involve other players if one player's magus is involved in secret house business. Of course, the Troupe style play is intended to have other players play NPC roles occasionally. And I have tried to delegate plot-modes out to players, with limited success.
And not only Mystery Cults give this challenge, other Houses' organizations or "social clubs" affect the saga the same way.
So I like reading about the use of Bjornaer mysteries.
I believe bears only actually hibernate in cold climates, mountaintops, et cetera. Bears living in temperate lowland regions tend to not hibernate. Of course, I'll be perfectly honest that my 'source' is 'I watched nature documentaries with my girlfriend last week'.
ADDED: Also, I do feel the mechanics for a hibernation should be comprable to Cyclic Magic, yes?
An alternative approach to Hibernation would be to have the character constantly suffering a number of fatigue levels during winter (or loses all of certain types of fatigue level, to compensate for the fact that they get extra fatigue levels in bear form).