Aquatic Lash

While a Black Sapphire is fastened to the circlet, one of the spectral weapons takes the form of a Trident imbued by the Elemental Plane of Water. If you hit a creature with this weapon, the creature takes an additional 2d10 cold damage and if you deal damage to it, you can reduce its Speed by 10 feet until the start of your next turn. If the creature is hit more than once by weapons that have this property, the Speed reduction doesn't exceed 10 feet.