Very rare magic weapon (longbow)
Property: You gain a +1 bonus to attack rolls and damage rolls you make with this weapon. When you use this weapon to make a ranged attack, you can swear aloud an oath: “Swift death to you who have wronged me.” The target of your attack becomes your sworn enemy until it drops to 0 hit points or until dawn, seven days later. You can have only one such sworn enemy at a time. When your sworn enemy drops to 0 hit points, you can choose a new one after the next day dawns. When attacking your sworn enemy with this weapon, you have advantage on your attacks rolls and deal an additional 3d6 damage on a hit. Furthermore, your attack rolls against your sworn enemy ignore cover, other than total cover, and suffer no disadvantage due to long range. While you have a sworn enemy, you have disadvantage on attack rolls against all other creatures, whether you use this weapon or a different one.
This longbow is snow white and, despite its slender profile, exceptionally strong. When an arrow is nocked to its string, the bow whispers to its wielder in Elven, “Swift defeat to my enemies.” Oathbows are carried by elf heroes, who receive them as gifts of esteem from a Faerie monarch. Elves who see an oathbow in the possession of a non-‐elf might assume the bearer stole it.