After all the Revisions the Houses went through I started to Wonder, and decided to ask a difficult (at least for me) Question here:
Would the 5th Edition Bjornaer´s Design a Spell like Avenging Beast ?
Thank you for your input..
(I also asked the same Question on the Ber(zer)k List).
I think it would be recognized as useful when you really need it, but also perceived as rather grotesque, especially in the case of non-combative heartbeasts: while magi with combative heartbeasts would only be further improving their natural combat prowess, turning a non-combative heartbeast into a combat ... monster ... thing is something of a mockery. Seeking your inner heartbeast, whatever it may be, would be so much more rewarding.
Only trouble that you need to get initiated sooo deeply....
(which isn´t so easy with established Characters who started without the Virtues necessary).
I've kind of been seeing the new spells adjusting the bodily humors as a 'finessed' of the Avenging Beast and that the old spell isn't gone due to finding it less appropriate to the new Bjornaers, but just that the humors spell is much more interesting and resonating with the setting than the old version.
Not to mention that it was grossly overpowered. 
There is that.
Where do i find The Avenging Beast , my search-fu has failed me. 
4th Edition?
Dragon &Bear
Houses of Hermes
For your convinience (a Quote from said books):
Form of the Avenging Beast (Mu/Co 20)
Spell Focus: Bodypart of the appropriate Animal (+2)
R: Per, D: Sun, T:Ind
The Shape of your Heartbeast becomes more powerful and deadly.
If you have a battleworthy Heartbeast you gain +5 on Attack and Damage
Rolls and +15 on Soak.
If your Heartbeast is not battleworthy ,it gains +3 on Attack and Damage
Rolls and +10 on Soak.
In addtion you receive no penatlties from accumulated
Body and Fatigue until you are unconscious, incapacitated, or dead.
Your Heartbeast becomes more ferocious, more fearsome, and larger, but
also slightly disorted.
After rereading...
It is overpowered for a Lvl.20 Spell.
Form of the Avenging Beast
MuCo(An) Level 30
R: Per, D: Sun, T:Ind
+03 is added to your Soak and +01 to Size
Your Animal form gains the Qualities of Extra Natural Weapons* (Claws and Teeth).
If your animal form already has these qualities , they increase to Large.`
You also gain Tough Hide giving +02 to Protection**
(Base 15 / +02 Sun / +01 Animal)
(page 118)
Level 15 : Make a body resistant to damage (+03 Soak) , page 132
** this Quality stacks with the Tough Virtue (+03 Soak) and the Thick Fur/Scales Quality (+01 Protection)
Why make this a MuCo spell with a An requisite. Why not just make a MuAn spell?
It affects the Bjornaer's heartbeast, which is an Animal target.
I went with the MuCo(An) because the possibility exists for other characters to have an animal form , e.g. skinchangers or lycanthropes.
An attempt to do a more general spell , rather than a Bjornaer specific one.
Fair enough, but I'm not certain whether you need to that for other skinchangers either. Conventional skinchangers are affected by Animal in addition to Corpus (Bjornaer Heartbeasts are affected by Animal instead of Corpus). So an Animal spell should work fine for both Bjornaer and Lycanthropes.
I guess if the shapeshifter loses the ability to cast spells when in their Animal form, the Corpus version might be required.
Another option could be a MuVi(An?) spell that modifies whatever supernatural power the character uses to transform?
As to MuVi affecting the transformation ability , the guidelines on page 159 , only allow for Hermetic spells to be affected.
Heartbeast is a mystical Ability and only has Momentary duration.
A Mythic Blood feat (page 47) is invoked as per a fast-cast mastered formulaic spell.
Fast Casting Speed : Quickness + Finesse + Stress Die (page 83)
(the feat could be a shapechanging one)
If these abilities are considered as Spontaneous , then a MuVi spell cannot affect them.
Timing is also crucial , and the MuVi caster has to fast cast to get the timing right , unless the target is co-operating.
MuVi spells that alter the Gift or mystical Abilities , do not seem to be covered.
Oh yeah. Good point.
It could be an idea for a research project though. Some sort of Virtue that allows you to affect (a particular) non-Hermetic magic for the cost of a magnitude (or more).
Also the justification for MuVi spells only affecting Hermetic magic is that "they depend on a good understanding of the processes involved." So I could certainly imagine a house rule which allowed a character to affect processes that he does have a good understanding of. A high Supernatural Ability Score, might be evidence of "a good understanding".
Even if using the abilities is "spontaneous", I don't think that is necessarily a problem in and of itself. The trick would be to affect the Supernatural Nature of the character rather than trying to interrupt an instance of the change as it happens. That is, try to affect his power rather than a use of the power.
That's a crazy idea for a muto vim magician.
They learn shape of the woodland prowler then they invent a muto vim spell to allow them to alter shape of the woodland prowler during casting into shape of whatever I darn well feel like.
Ja.
Lvl.30 is what I got myself doing the Math.(actually I was at Lvl.35 but i probably made an Error).
My Question is more a philosophical one then one concerning the math...
I think that it is absolutely doable to alter the hearbeast with Muto spells, no more difficult than altering your normal body with muto spells.
I think that philosophically it is no great dishonor to the ancestor spirit to change your own heartbeast form to be more martially powerful. My impression is that hte bjornear don't see the heartbeast as something other then themselves any more than they see their own body as anything other than themselves. If they won't have a problem casting gift of the bear's fortituse on their human form they won't have an issue with some fifth edition analoge to form of the avenging beast.
Maybe my next spell attempt should be Form of the Avenging Tree , for those with a Plant Heartbeast (page 22 , HoH:MC).
This could transform the character into a Triffid.
It's not overly addressed in canon, so I think it's largely up to the SG, Troupe and saga (as it should be.) However, don't confuse "concerned with animals and the bestial" with some sort of romantic druid-ish purity of nature (which would possibly be more along the interests of Merenita?)
The Mystery of the Heartbeast, the animal aspect that lies within some Magi and their relationship to that, is the focus of Bjornaer, not necessarily the animals themselves (except as a byproduct of that interest/connection.)