Longevity Rituals use Corpus, right? Could a Bjornaer Magi make one using Animal instead, and use it while in heartbeast form? I'm thinking about the Laws of Essential Nature. He really is an animal, and would be affected by animal magic. Any thoughts?
Eirik
Sounds nice in theory but as much as a Bjornaer is an animal while in heartbeast form, he is first and foremost a human magus. Without the magus there is no heartbeast, so I'd worry about keeping your magus alive first.
Animal would have no effect on the human form, so the magus would become decrepit very fast. IMO.
But the magus IS an animal in animal form. He can stay in this form as long as he wants, for years and years if he wants to. He can use magic, do laboratory stuff all in this form (with the help of certain spells to move things around, of course). So a Bjornaer is as much an animal as a human, complete balance.
Eirik
Longevity rituals are intensely personal to the magus. Animal for a Bjornaer - well, yes, of course... IMO.
I'd easily allow Ignem if your Inner Heartbeast were a phoenix...
chuckle ... the side effects could be interesting, of course.
My inner heartbeast is actually a water otter (anima). So Aquam would be interesting to use. But let's hope I don't need to do that in the first session. 
Eirik
Maybe I should go with a monkey heartbeast? Just so I can say "I will bring forth my Inner Monkey" at one point in the campaign 
Ehm... no.. 
Eirik
Monkeys in Medieval Germany? Now that would be a novelty! lol.
In a 4th ed. campaign I allowed people to use vis other than corpus for some of their longevity potion, with the understanding that using too much non-corpus could have odd effects. But then, we also ruled that whenever a magus improved an art to 10, 20 or 30 they gained some trait that hinted at it.
5th ed. has warping, so now I use that instead. But I'd still allow an amount of non-corpus vis... with some sort of cost. Like if a Bjornaer used Animal it might make him more inclined to stay in animal form rather than human or something.
Hmmm it's interesting.
On one hand, the use of other than Corpus might undermine the Corpus specialist, who thrives upon making Longevity Rituals for others. If the other Form possible depends on the USER and not just the creator, I'd hate to be the Longevity Master in Mercere... And perhaps it would give too much freedom for the non.Corpus specialists, who never again have to worry about Longevity.
On the other hand, having another Form to be close to your nature and personality, should rub off. Yes, it should add some odd results, and Warping is a good way of doing this. So, Mr Flambeau, you want to use Ignem Form for Longevity Ritual? Sure, it'll be easier than using your low Corpus, but it'll cost - in Warping.
Perhaps some sort of compromise, where Corpus isn't totally left out of the equation. E.g. if the substituta Form is never counted higher than 2xCorpus?
Note: We have House Ruled, than Requisities actually do this, rather than use the lowest of the two arts. So a Re(Mu)Te spell uses the lower of Re or 2xMu. In the cases of true requisites (e.g. shapechanging) we use the normal requisite rules, where two arts apply equally. The other methjod is only when one art is clearly secondary to the other.
Also, in my old saga (4th ed) we ruled, that up to 1/3 (or was it half?) of the vis in Longevity could be an Art integral to the nature of the maga. So if they were verye specialized, with Affinities etc. an Art appropriate for that would do the trick. The only drawback was, every Longevity Ritual after substituting vis in this was, needed to use the same percentage of the alternative vis! The rest could be in any of the normal combinations. We might do this in the new 5th ed saga also, seeing as how Corpus vis is always hoarded for medical emergencies.
In my own campaign, I'd say all magi except for Bjornaer would use Corpus. This is because of the law of essential nature, and Bjornaer magi are the only ones who can break it.
Other than that, a breakthrough would be needed. A big one at that.
Eirik
I'd leave non-corpus "longevity" to the mysteries or original research... And let it have somewhat different effects than the standard longevity.
After all, with the standard Creo Corpus you are keeping the physical form of a human in perfect shape. (Could have worked similarily with animal for bjornar, if it had not been for the fact that they were still on a human lifespan).
For say a Creo Ignem "longevity", you'd be keeping the flames in your heart ablaze... Might be a way to break the limit of restoring confidence points or fatigue...
But it wouldn't exactly extend your lifetime...
While a Creo Terram might extend your lifetime by a lot, but result in you being dormant most of the time...
Or be subject to violent tremors on occasion lol. 
CrHe rituals: the magus would bloom every spring/summer and wilt/"die" every autumn/winter. Pretty tiring cycle I would think and not too pretty for the covenfolk to behold.
Only with a breaktrough.
Creo Ignem longevity? Wtf? 
Specifically for Bjornaer and Animal... I'd say it's possible, but make the player work for it. Perhaps he can learn the technique from an old Bjornaer, who needs convincing...
For other Arts, and non-Bjornaer, I'd generally not allow any such thing. The art just don't fit, as ulf said. I might allow the use of related raw vis, though.
To add to my earlier post: I'd suggest adding the CrAn longevity as a Bjornar mystery... minor virtue I'd think.
There is also the argument that Otter lifespans (especially the European Otter) are relatively short (5 years on average for European species). So If one tailored their longevity ritual to their animal form might it not be logical to suggest that the human form would age faster as a result?
In my saga we allow to use another form instead of Corpus for magi, if they have a very special magical art that defines them, like Auram for our wind mage or Terram for our metal mage. We use this rule, because 1.) in most sagas it realy doesnt matter, because even low CrCo Lab Totals are good enough to let a magus live healthy till his early 100 and 2.) it fits the setting and the rules with form boni and such other things.
Well, I thought about this, and I added Difficult Longevity Ritual for my Magus. The whole "messing with the circle of life and death" issue doesn't sit well with this magus, also a reason to pick this flaw.
Most wild animals have shorter lifespans. An otter in captivity can easily reach 10-15 years. 
Eirik
I agree with ulf and Birbin.
There is nothing stopping a Bjornaer (or any other Magus) to conduct research on the standard formula so it can be modified and adapted to a magus's needs.
Making it a mystery would also work very nicely actually, and the mystery itself could have either been originated from a breakthrough or the incorporation of ancient shapeshifter rituals.
Sounds much more interesting and flavourful that way, but that may be just me. I love mysteries.
That's still considerably less than a human lifespan, so my previous question stands.
If you add to this the flaw "Difficult Longevity Ritual", I'd say you are rapidly heading for a brick wall. I think making this a Mystery you can learn (as others seem to agree) is your only viable option.