A quasi-necromantic idea is to use dead body parts as a form of substitution for lost limbs, as it is a popular fantasy trope. Many stories have similar myths, the one I like best is the Hand and Eye of Vecna from classic D&D.
Interestingly doing this in Ars Magica is not hard and might be achieve in a few ways depending on what the player wants. It is also probably better performed as an enchanted device.
Sensations of a New Hand
Intellego Imagonem 4, R: Touch, D: Concentration, T: Touch
This effect transfers the tactile stimulus experienced by the object touched (a replacement hand) to the caster; adding an additional source for tactile sensation. In effect the caster feels what the object would feel.
(Base 1 to use touch at a distance, +1 Touch, +1 Conc, +1 Touch sense)
Sensations of a New Eye
Intellego Imagonem 15, R: Touch, D: Concentration, T: Vision
This effect transfers the visual point of reference experienced by the object touched (a replacement eye) to the caster. In effect the caster can see magically from the eyeball, which is typically placed within an empty socket.
(Base 1 to use sight at a distance, +1 Touch, +1 Conc, +4 Vision sense)
The Obedient Hand
Rego Corpus / Intellego 20, R: Touch, D: Concentration, T: Individual
This spell allows a severed hand to be held against the stump and animated that hand as if it were a normal complete limb. The Intellego requisite allows the hand to respond in an intuitive manner to the needs of the body it is attached to.
(Base 4, +1 Touch, +1 Conc, +1 fine control, +1 Intellego)
I also started thinking how a Magus in Ars Magica might use a Rego spell and an illusion to replace their lost hand if healing spells were not their strength and necromancy was distasteful. The spell could be used for replacing any limb, or as an additional limb.
The Unseen Replacement Limb
Rego Terram 15, R: Voice, D: Concentration, T: Individual
This spell can manipulate objects at the caster’s desire, acting as a replacement or additional limb. The new limb has enough strength to pull against a resisting force or other object, with an equivalent strength of +0. The spell’s range allows for distant objects to be picked up and brought to the caster.
(Base 2, +2 Voice, +1 Conc, +1 additional strength, +1 living and non-living objects)
The Phantom Limb
Creo Imagonem 5, R: Touch, D: Concentration, T: Individual
This spell creates an illusion of a hand in the correct position for the target that moves appropriately for their actions.
(Base 1 for visual illusion, +1 Touch, +1 Conc, +1 for a moving illusion, +1 as directed by caster)
Each of the effects above are using Duration Concentration as the intent is to enchant a device to cast the spells and maintain concentration, or be a constant effect.
It is possible that a person could replace all their limbs with variations on these spells, or perhaps make a more complex variation which animated a group of arms and legs in one spell. The complexity (assuming it is +2 Group modifier from the hand animation spell above) becomes the same difficulty as animating a full corpse; which makes sense.
Enchanted Device – The NeverLost Hand
This enchanted device is designed to create the sense feeling and touch, which induces a deep sense of connection to the hand over time. The effect is cast by the hand onto the target who then feels that any movement made by the hand is as real as their own. In effect this makes the target feel as the hand would.
Spell: The Obedient Hand (above) modified as a constant effect (Ars Magica p.99), which alters the spell to ReCo/In 29 in the enchanted device.
Spell: Sensations of a New Hand (above) modified as a constant effect, which alters the spell to InIm8 in the enchanted device.
It is also possible that the enchanted device which holds these powers could be made to touch the objects to affect them rather than invested in the limb itself. It would not alter the spell designs, and would also allow the powers to be used on a variety of limbs or eyes, etc.
And lastly an unrelated effect to destroy an animal corpse.
Dust the Shambling Hound
Perdo Animal 15, R: Voice, T: Individual
This spell destroys an animal corpse, affects up to size +1 corpses which are not controlled by an independent spirit.
(Base 5, +2 Voice)
Find these and many more new spells for Ars Magica in my grimoire.