While I agree that transforming a willing target should be easier than an unwilling one, I completely disagree with you on how it should be done. For the purposes of a spell, the caster would have to meet a complexity equal to all his possible consequences plus 1, but doesn’t need to overcome his Stress Track, and his defense rating is locked at Mediocre (+0) (because he’s not trying to resist the spell or defend against it in any way).
That would set the base complexity for the spell at 21: 2 for his minor consequence, 4 for his moderate consequence, 6 for his severe consequence, 8 for his extreme consequence, and 1 to take him out.
Just for the record, I wasn't suggesting that transformations should be based on taking someone out. I was actually pointing out how *easy* self transformations would be if that was how it was defined. Offensive transformations use that format because really the purpose of the spell is to 'take someone out' and the fact that it's a transformation is really special effects more than anything else. A spell to destroy someone's mind would follow exactly the same format, but the FX would be different. Or ... perhaps a spell to rip someone's heart out? Same thing, different FX.
The spell we're talking about here has similar FX as the offensive transformation, but my take is that it's a totally different spell that merely looks the same. So the complexity should be based on the benefits granted by the benevolent transformation, because the spell is about granting benefits, not taking someone out.
I found an older thread in which this question was raised, and it pointed to the section in the rulebook that sort of handles this. See YS92, the "Temporary Powers" sidebar. Basically, thaumaturgy would become an excuse to make use of the rules in the sidebar to give you powers temporarily. If, for example, you wanted to turn into a normal animal, it would cost you 1 Fate to gain Beast Change [-1] for a scene, and you'd use thaumaturgy to enact that change. If you wanted Mythic Strength [-6], it would cost 6 Fate points. A player can 'owe' the GM some compels in place of some of the Fate points.
At first I wasn't happy with this, but I think it's starting to win me over. It doesn't give a "complete" system for using it as a system for Biomancy, though, so here's my attempt to round out the edges (borrowing from the post linked above) for using the sidebar in conjunction with Biomancy:
If you wish to grant temporary powers via Biomancy, begin by listing the powers you wish to grant. Sum up their refresh cost. The base complexity for the spell is two shifts per refresh (for a transformation that lasts one scene). The duration of the spell can be increased by a level on the time chart per shift added to the complexity. Once the complexity is known, the spell is cast as usual for Thaumaturgy.
In addition, the target (either you or a *willing* subject) gains a point of 'Biomantic Debt' for every two points of complexity. Biomantic Debt represents the physical (or even non-physical) wear and tear on your body (or mind) by pushing it further than it was meant to go. Each point of Debt gives the GM a free compel, which can be used any time after the spell duration ends. The target does not get a Fate point for these compels, but may buy out of a compel by paying a Fate point. Some example compels might involve strained muscles from improved strength, or animal-like behaviors left over from shapechanging into an animal.
Some examples:
Giant's Strength
Need to lift a car, but don't have a forklift handy? Know of a monster that *really* deserves a major smackdown? Well, now you can do these things and more with better living through Biomancy!
Type: Thaumaturgy, biomancy
Complexity: 8 shifts (more for longer duration)
Duration: One scene
Effect: Willing target gains 4 point of Biomantic Debt, and also gains the effects of Supernatural Strength for the duration of the spell. Note that this particular version of the spell does not increase the target's size.
Thaumaturgical Werewolf
The Alphas have all the fun, but that need not be the case! No wolf pelts or demonic assistance required, though it might make the spell easier...
Type: Thaumaturgy, biomancy
Complexity: 16 shifts
Duration: Until sunrise or sunset
Effect: Willing target gains 8 Biomantic Debt, as well as the abilities of a werewolf (Beast Change [-1], Inhuman Strength [-2], Inhuman Speed [-2], Claws [-1]) and can change back and forth into werebeast form for the duration of the spell. While not in werebeast form, the target loses access to the other werebeast powers. Note that this spell does not include the senses or instincts of a true werewolf, which require considerable time and practice to learn to interpret.
Thoughts?