Greyblade

Weapon (any sword), legendary (requires attunement by a warlock or eldritch knight)

These ancient blades have served warlocks for centuries if not millennia. Their origin has been lost to time and legend, but they are recognized as potent armaments. The sword has an ornate hilt set with an eye-like agate, and a dull, grey blade engraved with symbols. You gain a +2 bonus to attack and damage rolls made with this magic weapon.

In addition, you can make one attack with it as a bonus action on each of your turns.

As an action, you can target all enemies within 30 feet you can see with a curse. Each target must make a DC 15 (or your warlock spellcasting DC, if higher) Wisdom check.

On a failure, the creature is affected as by bestow curse for a duration of 1 minute. You can choose any bestow curse effect but must choose the same curse for all targets. You must finish a long rest before using this curse ability again.