Half breeds and a Human
This is a +2 dagger that heals the user 1hp per hit dice of any creature killed with it (minimum 1). Any creature killed by this weapon, if raised to undeath comes back with 10 additional permanent hit points. This weapons detects as evil.
This ancient dagger, and many like it have been used by the Ulher in their sacrifices and dark magics for centuaries. Every one of them has gained some ability based on how it is regularly used.
This particular blade has a strong tie with undeath, its wielders draw the last strength from their victim while binding them together, making is easier for them to call them back from the dead as servants.