Water Banshee

Detect Life. The banshee can magically sense the presence of creatures up to 5 miles away that aren’t undead or constructs. She knows the general direction they’re in but not their exact locations.

Ethereal Currents. The banshee can move through other creatures and objects as if they were difficult terrain and gains the ability to move through water effortlessly. It can travel through any body of water without impediment, and it has a swim speed equal to its flying speed.

Corrupting Touch. Melee Spell Attack: +4 to hit, reach 5 ft., one target. Hit: 12 (3d6 + 2) necrotic damage.

Abyssal Drench (Recharge 4-6). Each non-undead creature within 60 feet of the banshee that can see her must succeed on a DC 14 Dexterity saving throw  taking 4d6 cold damage and becoming soaked for 1 minute on a failed save. Soaked creatures have disadvantage on Dexterity saving throws and Dexterity-based attack rolls.

Drowning Wail (1/Day). As an action, the banshee releases a haunting wail that resonates with the element of water. All creatures within 30 feet that can hear the banshee must make a DC 15 Constitution saving throw or be magically restrained as water wraps around them. Restrained creatures can repeat the saving throw at the end of their turns, ending the effect on a success.

Aquatic Phantoms: The banshee can summon spectral water creatures to aid it in battle. As a bonus action, the banshee can summon 1 water spirit within 20 feet. These spirits act on the banshee's initiative and have the same statistics as a Water Weird except they disappear after 1 minute or when reduced to 0 hit points.