In the Open Grave supplement for 4E are undead grafts.
For example zombie arm, wight's claw, mummy's eye, etc.
They usually give additional power at the expense of undead vulnerabilities.
Meaning the creatures that have undead grafts gain a vulnerability to radiant damage.
Why stop there?
If it is possible to graft undead body parts, living body parts should
be possible as well.
Here is list of possibilities:
- Beholder's eye - gain eye beam power
- Basilisk eye - gain petrifying gaze
- Scorpion tail - gain poison sting attack
- Dryad Claw - gain claw attack and treestride (teleport next to plant)
- Medusa eyes - gain petrifying gaze
- Rust Monster stomach - gain ability to eat magic items
- Angel wings - gain Fly ability
- Shambling mound tendrils - gain regeneration and lightning affinity
Depending on the compatibility between the graft and the creature receiving the
graft there may be disadvantages.
Grafting isn't widespread, it takes a high Heal and Nature skill
to pull it off.
D&D 3.5 has more graft possibilities than 4E:
see Stitching Things Together: The Graft Handbook
Where the grafts are placed
Eyes can be placed anywhere:
- large eyes on the chest
- small eyes on arms or topside of hand
Why limit a creature to only two arms or one tail?
For example: the Skeletal Tomb Guardian found in the monster manual.
Used for PCs or NPCs
Grafts should only be used on NPCs.
Using grafts creates unique NPCs with surprising powers
and weaknesses. An example of a grafter is Valna, Elven Druid.
I think it's a bad idea to give to PCs as a reward.
As a punishment grafts could work, like the ones in Open Grave.
The idea of someone putting grafts on the PCs to make them do
what the grafter wants is interesting, but it's best that
the players are on board with that idea first.