Nine Lives Stealer

Weapon (Any Simple or Martial), Very Rare (Requires Attunement)

You gain a +2 bonus to attack rolls and damage rolls made with this magic weapon.

Life Stealing. The weapon has 1d8 + 1 charges. When you attack a creature that has fewer than 100 Hit Points with this weapon and roll a 20 on the d20 for the attack roll, the creature must succeed on a DC 15 Constitution saving throw or be slain instantly as the sword tears its life force from its body. Constructs and Undead succeed on the save automatically. The weapon loses 1 charge if the creature is slain. When the weapon has no charges remaining, it loses this property.