Ammunition

Very Rare

Named: When chambering this enchanted round, the shooter chooses a creature within firing range that they can see. The bullet then becomes imprinted to that target, gaining advantage the attack roll against it and automatically turning a hit into a critical hit. Attacks with the bullet have disadvantage against every creature other than the designated target.
The bullet can be reset after seven days or if the designated target dies.

They say that a bullet has a name on it.
The weaponsmith behind this line of ammunition took this literally and enchanted every single one of them with magic that makes them aggresively home in on a designated target, making them the perfect tool for assassins.