@stjepanlukac first solution reminds me a villain I put against the party, a pirate necromancer in al Qadim. He lost his arm in battle and somehow revived it and put it again back. But the arm has a necrosis and is going to trasform the villain into an undead. It has powers and at the same time changes his personality. (It was thought for a villain that could return back some time after, changed)