Source: Dungeons and Dragons - Honor Among Thieves

Weapon (dagger), legendary

Forged by Red Wizards using a secret process known only to them, this grim steel dagger draws its power from the Negative Plane. When you hit a creature with a melee attack using this magic dagger, the target takes an extra 3d12 necrotic damage.

A creature reduced to 0 hit points by this weapon dies and can’t be raised from the dead except by a deity or by a creature using a tablet of reawakening to cast the True Resurrection spell.