Bloodthirsty Weapon

Weapon (any weapon that deals piercing or slashing damage), rare (requires attunement)

This magic weapon bears long, branching channels inscribed into its blade or head, and it gives off a coppery scent. When you damage a creature that has blood with this weapon, it loses an additional 2d6 hit points from blood loss.

Thirsting. The weapon acquires a taste for creatures it damaged. When you miss an attack with this weapon against a creature you damaged with this weapon within the last 1 minute, the target loses 2d6 hit points due to blood loss as the weapon draws blood out of open wounds as it passes. If the wounded creature uses an action to stanch the wound with a successful DC 15 Wisdom (Medicine) check or the creature receives magical healing, the blade no longer has a taste for it, preventing this property from triggering. This property doesn’t work against creatures that don’t have blood.