Thank you to Theomund for the comment on another post which started me thinking about the limits of what Muto Corpus / Animal spells can do, and what the guidelines imply. Initially the suggestion was to use the gorilla as the base animal, however I’ve used a bear in the naming as I think bears are more prolific in medieval Europe and the bear has a very high strength star in the Book of Beasts.
To begin an answer – the MuCo2 baseline which is commonly used for minor transformations an abilities seems far too low to allow for a wholesale change. A full transformation into an animal is MuCo10, and birds or fish is MuCo20, and the themes of Ars Magica seem to imply that moving to a know form (wolf, bird, etc) is easier than a partial or unknown form. So I think a Muto Corpus 15 base is better to represent this type of hybrid man/animal transformation. The transformation might grant a few new attributes or adjustments as long as the additional powers or aspects are very similar and thematic. Further additional magnitudes should allow even more strange abilities, such as combining attributes from different animals.
This is aligned with Gift of the Bear’s Fortitude, which uses a MuCo15 base, which transforms all of the target’s body to grant a combat mechanic advantage and does not use an Animal requisite.
This is very similar to what I suggested for the Monstrous Transformations of Behemoths and Dragons and also in a Discussion on Muto Transformation Magic in an earlier posts:
(based upon the appropriate guideline for land or sea/air animals) … 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.
This means that once the base level has allowed for an animal transformation, an additional magnitude should allow for a strange transformation (making a rough new MuCo Baseline of 15 for partial transformations), and then a further magnitude should allow for a good spread of physical abilities. I think it’s logical to use the same spells as a guide for a hybrid form; as that is basically what the Behemoth was.
Aside – There has not been a Muto Corpus spell which adds to a stat, probably as it is covered by Creo Corpus although the Ars Magica system seems to allow for many different ways to achieve an end.
New Hermetic Baseline – Muto Corpus 15 – Allows a partial transformation of a human to a land animal, granting aspects of both the animal form and human form. Requisites are probably needed.
New Hermetic Baseline – Muto Corpus 25 – Allows a partial transformation of a human to a sea or air animal, granting aspects of both the animal form and human form. Requisites are probably needed.
A spell transforming with an aspect of animal strength might be as follows. This uses a “partial transformation” of MuCo/An15. This is a useful spell as it allows the target to continue to use human sized weaponry and armor against targets, and not suffer a limitation of striking MR due to an active spell (discussed here).
Gift of the Bear’s Strength
Muto Corpus / Animal 30, R: Touch, D: Sun, T: Individual
Changes the target’s body to gain the broad musculature of a bear which enhances their frame, increasing Strength by +3. Equipment and clothing are not altered by this spell and may no longer fit suitably.
(Base 15, +1 Touch, +2 Sun)
A spell to transform into a hybrid creature might be:
Form of Hulking Werebear
Muto Corpus / Animal 30, R: Personal, D: Sun, T: Individual
Transforms the caster into a chimeric blend of man and bear, resulting in a large bipedal hybrid. The humanoid form increases in size by 2 to a maximum of Size +2, retains rudimentary humanoid head, hands and feet, although the gross shape and size change causes most equipment to be difficult to wear. Replace all physical attributes with those of an adult bear (Strength, Stamina, Dexterity, Quickness, and Size) and average Perception, Awareness, and Communication. The bear’s natural claw and bite attacks are halved in effectiveness. Equipment and clothing is not altered by this spell.
(Base 15, +2 Sun, +1 additional attributes and bear themed abilities)
Related link on Ars forums http://forum.atlas-games.com/viewtopic.php?t=32533, and other custom spells for Ars Magica can be found on the new spells page.