Oathsword

Weapon (any slashing), rare

This sword shimmers with many colors when held in direct sunlight. When in combat, you may say the words “Marked Enemy” and choose any creature within 60 feet of you. That creature becomes your Marked Enemy until it is slain or for one hour, whichever is sooner. You gain a +2 bonus to all attack rolls against your Marked Enemy, and your first attack against it is with Advantage. You may only have one Marked Enemy at a time.