Dagger of the Death Cult

Weapon (dagger), rare (requires attunement)

This dagger appears made from shards of bone melded together by unnatural means, with a small femur for a handle. You gain a +1 bonus to attack and damage rolls made with this weapon. If you attack a restrained creature with this dagger, you deal maximum damage.

If you attack an incapacitated creature with this dagger, the creature takes maximum damage and must make a DC 15 Constitution saving throw. On a failure, the creature immediately loses all hit points and begins making death saving throws. If you deal damage to a creature that is making death saving throws and use this dagger, they immediately die and their soul is stored in the dagger. Only one such soul can reside in the dagger, and a special ritual must be performed to remove the soul for more unsavory purposes.