This effect grants the target animal’s hide and fur mythical toughness, expressed as a +9 bonus to Soak. The Terram requisite is present to allow for strength beyond what is possible for strengthened fur and hide."
So what do you think about It. I do see It tries to give you effectively the heaviest metal armor's damage resistance. I think the CrAn spells yo give you damage resistance are for that same purpose. Could you do It with corpus too? Why would you use CrAn por CrCo the ever to achieve damage resistance?
Spell is HR. MuAn can use MuCo Bases, which if you look comes out to +1 Soak for every 5 levels of the Base (5 = +1, 10 = +2, 15 = +3).
The description for using Terram makes no sense, the published Bases go up to Base 25 for +5 soak which is a higher Base used in the spell. If the SG ruled that Base 25 was the highest you could go with MuAn/MuCo then the addition of Terram might be acceptable for a higher magnitude. However using it to generate a soak total that would require a Base 45 with a Base 15 is pretty balance breaking.
As I said in another thread the tome is best used as a source of inspiration for spells/effects rather than an actual source of game ready spells/effects.
I would just add on that using Guideline from Animal for Corpus or vice-versa will work most of the time (most of the time - important to notice) and it is mentioned in the some book to proceed so. But using guideline from any other form to apply it on Corpus is dodgy at best, or would likely lead to crazy stuff in most case.
And I could not find a guideline in Terram allowing to improve toughness of material - although you could use Base 4: Changes dirt so that it is highly unnatural and use it to make something unbreakable, which is not the same as infinite soak, by the way.
