Multiattack

The River King makes two Longsword or Flood Blast attacks.

Longsword

Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 5) slashing damage, or 10 (1d10 + 5) slashing damage if used with two hands, plus 10 (3d6) poison damage.

Flood Blast

Ranged Spell Attack: +8 to hit, range 120 ft., one target. Hit: 21 (4d8 + 3) bludgeoning damage, and the target must succeed on a DC 18 Strength saving throw or be pushed up to 30 feet away from the River King and knocked prone.

Grasping Whirlpool (Recharge 5-6)

The River King magically creates a swirling vortex of water centered on a point he can see within 60 feet. The vortex appears in the shape of a cylinder that is 15 feet tall with a 10-foot radius. Each creature in the area must make a DC 18 Strength saving throw. On a failure, a creature takes 36 (8d8) bludgeoning damage and is restrained. On a success, a creature takes half the damage, isn't restrained, and can choose to be pushed out of the whirlpool's space. A creature that chooses not to be pushed suffers the consequences of a failed saving throw. While restrained, a creature is unable to breathe unless it can breathe water, and it must succeed on a DC 18 Strength saving throw at the end of each of its turns or take 18 (4d8) bludgeoning damage. A creature, including the restrained creature, can take an action to free the restrained creature by succeeding on a DC 18 Strength check. A creature with a swimming speed has advantage on the saving throw and on the Strength check to escape.

Spellcasting

The River King casts one of the following spells, requiring no material components and using Charisma as the spellcasting ability (save DC 16): At will: create or destroy water, water breathing 3/day each: freedom of movement, control water 1/day: control weather (as an action)