Damn, if only the baka anuki had some major ability to create artificial limbs to use in the ritual... Oh, wait, they have.
Anyway, it's pretty clear by now that the ability can and will create plenty of fringe cases, since again, the monster classes were never designed for taking in account there's something else that can cherry pick them at will. The abilities are too varied. The prerequisites are too varied. The penalties are too varied.
And this will forever slow down monster class design, because every time a new class comes out, I have to take in mind "This ability is cool, but baka danuki can pick this and combine it with X out of the blue, so it needs to be nerfed"
You. Cannot. Make. This. Work. Without. Remaking. Everything. Else. From. Scratch. Point. Just scrap it off or make it based on basic polymorph.
EDIT: Or another possibility, you simply make a custom list of abilities for the baka-danuki to pick from. Breath weapon, shell, rays, special movement, etc.