Bloodthirsty Dagger (3.5e Equipment)
From D&D Wiki
Bloodthirsty Dagger: Once a player or NPC holds the weapon in their hand (bare or gloved) they must make a DC20 Will save or become bonded to the weapon. If save is successful nothing happens. Must make a new save everytime the weapon is picked up. If save fails then the player cannot put the dagger away, drop it or remove it from their hand in anyway until it has shed some innocent blood. This means player cannot cut themselves or anyone volunteering themselves to be cut to satisfy this bloodlust.
For every 10 rounds the player holds the dagger the bloodlust becomes stronger and the more blood is needed and remember 1minute = 30 roundsnatwat. (IE first 10 rounds a single strike to a victim satisfies it, rounds 11-20 must successfully use it twice, rounds 21-30 must successfully use dagger 3 times on unwilling victim and so on). The bloodlust is not satisfied with undead blood or dead blood.
Once the bloodlust is satisfied then the player can drop, give away, sell, place in pack or anything else they want with the weapon.
The more the player uses the dagger, the more they want to use it and more they want to use it on pure innocents (IE children, the non-combat baker, the old lady down the lane, etc).