MuCo/An - Only the form of a magical creature

I'm interested in transformation effects, and have a query about "hybrid" or "unnatural" creatures (and yes, I've read the Firelord post for changing to a Dragon. I didn't want to necro that thread).

I'm talking about changes to the physical form, and excluding any magical powers, or Mights score. So the magi gains powers which are related to the physical form (gills from fish, pulling power for horses) but no fire breath, etc.

A spell can change the caster into a natural land creature at MuCo/An base 10, a bird of fish at base 20. Understand you get the physical benefits of the new for, but no implied magical powers. If cast with foci you can end the spell at will.

I'd like my character to design spells for unusual creatures; and also to design creatures which are hybrids of many creatures. So I was trying to suss the MuCo/An guidelines as relates to MuAn for hybrid creatures (hopefully I'm explaining my logic and question well enough).

  • a unicorn is physically just a Horse with a horn on it's head (ahem), so still base 10 for Muto Corpus/Animal for a horse; then boosted by +1 mag for a size +2 creature.
  • The related MuAn guideline seems to be a minor unnatural effect on a horse as base 5. Is the horn worthy of a +1 mag change, because it is small and unnatural, or should the horn be "free" for a designed effect?
  • then extending on that - to a major unnatural effect for an animal using MuAn to grant claws, fangs, and scaled armor is base 15 on a land animal using MuAn. I'd assume the same level applies for MuCo/An 15, to change a human into a creature with enhanced claws, fangs, etc. It looks like MuCo/An 10 is land animal, so major change to land animal form as part of a human's transformation is MuCo/An15.
  • then extending on that type of effect where a bird or fish was "enhanced" using the guidelines to apply to a fish or bird, is around MuCo/An 25 because the base for fish/birds is 20. So altering a Dolphin to grant sharp teeth and razor fins is MuAn15, or turning a human into the same ghastly dolphin is MuCo/An 25.
  • This is where I am not sure if the effect should be +1 mag for the major change of the target creature when doing a Muto Corpus effect, or +2 mags. Is the base effect for Muto Corpus high enough to justify the alteration of the form at +1?
  • giving a human wings initially seems no worse than a full transformation, but it appears trickier. I can accept that in the setting because an animal is a "known natural form", where a "winged human" is unnatural. So MuCo25 base for human targets. Assuming the wings are big enough, they should be able to fly.
  • lastly throw together a set of skin from an alligator, claws from a lion, wings from a hawk, huge mouth and teeth from a lizard, improved night vision from a cat, and all sorts of "draconic" changes into a Muto Corpus/Animal spell, where each sub-set is inspired from an animal - where does that leave the spell level? It would seem to still be Base 20 for Bird, +1 mag for major unnatural changes. Then perhaps +1 mag for "increased complexity" due to throwing them altogether. So Muto Corpus/Animal 30 for any combination of monstrous abilities and form, as long as the target creature is still human sized.

Is a symbol/shape/picture of the creature enough to form the foci for the purposes of cancelling a spell?
i.e. I can't get a Unicorn horn easily, but I could design a spell to take the shape of a unicorn by having a toy unicorn, or drawing which is dropped.?