A core rulebook spell in Ars Magica is The Severed Limb Made Whole which allows a limb to be reattached, but it cannot assist if the limb has been lost. The spell below addresses the times when the part of the target is missing and will need to be regrown.
Regrow the Misplaced Limb
Creo Corpus 30, R: Touch, D: Momentary, T: Individual, Ritual
This spell allows the target to regenerate a lost segment of their body. The spell can restore a single missing aspect of the targets body, be that a limb, hand, nose, or whatever.
(Base 25, +1 Touch, Ritual)
Aside – I imagine this spell would be a must have for games inspired from GRRM’s A Song of Ice and Fire or Star Wars as both those stories have character with missing limbs all over the place. You’d think there was a secondary market.
As far as complexity is concerned it seems as difficult to heal a major wound as it would be to reattach a limb, so the base of the spell is the same as SLMW. And nice for a change to write a quick and useful effect which doesn’t need a lot of interpretation of the spell guidelines.
The Severed Limb Made Whole is an odd spell as it contains a negative complexity modifier; which is exceedingly rare in Ars Magica. Generally that is not done at all, and I’ve no idea why a core spell would do that unless it was to keep it in line with a version from a previous edition.
This and over 300 other new spells for Ars Magica can be found here.