Sahuagin Wave Shaper

The wave shaper has advantage on melee attack rolls against any creature that doesn't have all its hit points.

The wave shaper can breathe air and water, but it needs to be submerged at least once every 4 hours to avoid suffocating.

The wave shaper can magically command any shark within 120 feet of it, using a limited telepathy.

The wave shaper makes two attacks: one with its bite and one with its claws.

Melee Weapon Attack +4 to hit, reach 5 ft., one target. 10 (2d8 + 1) Piercing damage plus 13 (3d8) Cold damage.

Melee Weapon Attack +4 to hit, reach 5 ft., one target. 10 (2d8 + 1) Slashing damage plus 13 (3d8) Cold damage.

The wave shaper targets a body of water at least 50 feet square and 25 feet deep, causing a whirlpool to form in the center of the area. The whirlpool forms a vortex that is 5 feet wide at the base, up to 50 feet wide at the top, 25 feet tall, and lasts for 1 minute or until the wave shaper is Incapacitated. Any creature or object in the water and within 25 feet of the vortex is pulled 10 feet toward it. A creature can swim away from the vortex by succeeding on a DC 14 Strength (Athletics) check.
When a creature enters the vortex for the first time on a turn or starts its turn there, it must make a DC 14 Strength saving throw. On a failed save, the creature takes 9 (2d8) Bludgeoning damage and is caught in the vortex until it ends. On a success, the creature takes half damage and isn't caught in the vortex. A creature caught in the vortex can use its action to try to swim away from the vortex as described above, but it has disadvantage on the Strength (Athletics) check to do so.
The first time each turn that an object enters the vortex, the object takes 9 (2d8) Bludgeoning damage. This damage occurs each round it remains in the vortex.