Thoughts on the Muto Corpus spell guidelines in Ars Magica

I’m doing a lot of thinking about Muto effects in Ars Magica, and part of the pondering led me to find that generally speaking the Muto Corpus effects were a little harder than the Muto Animal effects, and that there seemed to be a tolerance for adding strange limbs and such in Animals which wasn’t as clear when performed on Humans.

Err, yes, this is another highly specialised Ars Magica blog post, dealing with transformation spells.

I started with the idea of changing a man into a horse, which is stated clearly in the gudielines as MuCo/An level 10. There is also the guideline in the Animal section which talks about adding a useful minor ability to an animal being base level 5.There is also the general spell guideline which states than a related minor power can be added as part of a spell effect by adding a magnitude (+5 levels).

So it seems to be +5 either way. Cool.

A Major unnatural effect on an animal is Base 15, which is saying basically that an animal can be transformed into almost anything animal-ish at level 15. It is certainly harder to make a monster than to transform an animal into another form, which is only level 10. Then at level 25 are radical changes to animals (such as wings and all sorts of crazy stuff I’d expect).

The guts of the question is in this sentence:

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.

The base to morph a human to a land animal is level 19, and a fish or bird is 20. This makes a kind of sense, being that it sounds harder to turn a human into a monster dolphin, than to just turn them into a dolphin. And harder to turn into a fish or bird, than a dog. And it certainly follows that turning a man into a dolphin is tricky.

Then I got into what it would take to turn a human into a Dragon-ish creature. The closest base I could find was MuCo20 for a flying creature, then modified upward for the range of fangs, claws, poison bite, gills, night vision eyes, and such that make a draconian form so intimidating.

…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.

This ends with a MuCo effect of 30 which allows the caster to tailor a wide array of abilities from a range of beasts into one form. That is the same complexity in the rules as turning a human into an insubstantial form.

Question – Does this type of change need to be +1 mag for major unnatural changes AND +1 mag for “increased complexity”? Or can the same side effect adds +1 mag rule from the Unicorn’s horn above apply here to make this +1 mag modifier total, rather than +1 and +1?

Having the increased complexity pays a little more so makes it harder to refute, but it could be over paying. As the player of this character I want this as cheap as possible, but as a GM I’m pondering if it should be harder.


  • +1 mag for major unnatural changes” means a few, but not too many. Or a few that all follow a similar theme.
  • which then gives weight to “+1 mag for increased complexity” to generally allow crazy stuff.

I think I’ll go with that. A few similar thematically alterations only cost +1 mag, but many will cost another +1 mag. So the extra +1 mag allows for say 12-15 powers, where the limited one allows for a few.

Expensive, but harder to argue against.


Ref: As asked on the forums

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.


2 thoughts on “Thoughts on the Muto Corpus spell guidelines in Ars Magica

  1. Pingback: Transformation into Gargantuan Creatures, Part One | The Iron-Bound Tome

  2. Pingback: Gift of the Bear’s Strength, and Hybrid Transformations using Muto | The Iron-Bound Tome

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