Oathbow of Infinite Thirst (5e Equipment)
From D&D Wiki
weapon (longbow), very rare (requires attunement)
When you nock an arrow on this bow, it whispers in Elvish, “Swift defeat to my enemies.” When you use this weapon to make a ranged Attack, you can, as a Command phrase, say, “Swift death to you who have wronged me.” The target of your Attack becomes your Sworn Enemy until it dies or until dawn seven 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.
When you make a ranged Attack roll with this weapon against your Sworn Enemy, you have advantage on the roll. In addition, your target gains no benefit from cover, other than total cover, and you suffer no disadvantage due to long range. If the Attack hits, your Sworn Enemy takes an extra 3d6 piercing damage.
While your Sworn Enemy lives, you have disadvantage on Attack rolls with all other Weapons.
Curse of Infinite Thirst
This Weapon is cursed. Although not sentient, the Oathbow of Infinite Thirst is possessed by a vicious and voracious demonic spirit. The spirit curses you for attuning to this longbow and you cannot attune to another Weapon until you are targeted by the Remove Curse spell or similar magic cast by a fey or celestial creature. Anyone targeting the bow with the Remove Curse spell breaks the attunement but does not end the spirit’s curse on you.
While attuned, it functions like an Oathbow, but the spirit demands blood. They take a sip of your blood (you take 1d4 slashing damage) when you shoot your first arrow after dawn targeting a living creature that has blood. They take an additional sip for every arrow you loose at a Sworn Enemy. If not fed a sip of your blood for more than a day or seven dawns pass without using the bow to kill a Sworn Enemy that has blood, when you nock an arrow, the spirit angrily growls in Abyssal, “Sate my thirst for an enemy’s blood.” After which, they will not let you choose a Sworn Enemy until the dawn after the bow is used to kill a living creature that has blood.
At dawn every day your Sworn Enemy remains alive, the spirit starts taking bigger sips of your blood (each sip’s damage increases by 1d4 per day). This additional damage persists until you use the bow to kill a Sworn Enemy that has blood. If your Sworn Enemy lives to see seven dawns, the spirit curses you and you continue to have disadvantage on Attack rolls with all other Weapons. If the attunement ends before the seventh dawn, the spirit’s curse can be avoided. However, once that seventh dawn passes, you are thusly cursed and remain so until you use the bow to kill seven Sworn Enemies that have blood or the curse is removed with a Greater Restoration spell or similar, more powerful magic cast by a celestial. Alternatively, a fey casting the Banishment spell on the bow forces the spirit to leave it, ending all curses they put on you. After the spirit is driven out, the bow still counts as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage, but has no other properties.