Oathsworn

Weapon Enchantment, Very Rare (requires attunement)

When you use this weapon to make an attack, you can utter or sign the following command words: “Swift death to you who have wronged me.” The target of your attack becomes your sworn enemy until it dies or until dawn 7 days later. You can have only one such sworn enemy at a time. When your sworn enemy dies, you can choose a new one after the next dawn. While you have a sworn enemy, the following properties apply:

Attacks Affected. You have advantage on your sworn enemy, and disadvantage on attack rolls with all other weapons.

No Cover. Your sworn enemy gains no benefit from Cover. If you’re making a ranged attack, you suffer no disadvantage due to long range.

Extra Damage. Your sworn enemy an extra 3d6 damage from all attacks made with this weapon.