In an old discussion on RPG Stack Exchange I suggested a virtue to allow an enchanted device to also be a symbiotic link to the caster as part of a form of necromancy, and blogged about it too. Here is the shorter version.
Symbiotic Invested Devices (Hermetic) +1
By use of this virtue the magus can create invested devices which are symbiotic links to the creatures they are used by. The invested device must still use the limiting Arts (use appropriate effects to facilitate the function of the device itself as relevant) and the item is further enhanced by this virtue to feel like a natural part of the target.
A sample use of this virtue would be a replacement hand for a magus who lost theirs in combat. The hand forms such a visceral link to the user that it functions as a normal hand (or perhaps even better than).
The virtue may be used on any type of targets (subject to Art requirements) such as men, animals, or even trees, and may add new functions to existing creatures; such as wings on a human as crafted for Icarus. It is worth noting that devices crafted in this manner are better than prosthetic replacements in that they actually feel like a part of the target creature.
e.g. The NeverLost Hand – this enchanted device is designed to create the sense feeling and touch, which includes a deep sense of connection to the hand. 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. An important note is that the hand itself has no invested powers that facilitate movement, which means that the most effective way for the target to feel these experiences is to hold and move the hand themselves, or give it to another.
A “normal” item without the creator having this virtue would be crafted with two effects:
a InMe effect around level 30-35, (Base: 4 (?), +1 complexity in feedback to target, +2 Duration Sun, +2 Range Voice, nn uses per day +3, etc)
a ReTe effect around level 15-20, to move the hand as the wearer desires.
This virtue removes the need for the first effect.
There are restrictions on the devices:
the device only functions properly when placed upon the wearer. This means that a replacement hand is no use to a person who already has a hand.
the devices cannot heal as normal, and damage must be repaired.
Amongst the potential for devices is all sorts of more traditional items from other games, such as the Hand and Eye of Venccna from DnD Greyhawk lore, the Steel Arm from DragonLance, and so on.
In the end this might be just another funny and odd virtue for Ars Magica, which I hope to use one day on a character of mine.