Aquathorn Serpent

Aquatic Camouflage. The Aquathorn Serpent has advantage on Dexterity (Stealth) checks made while underwater.

Thorned Hide. Any creature that hits the Aquathorn Serpent with a melee attack while within 5 feet of it takes 2 (1d4) piercing damage from its thorns.

Water Breathing. The Aquathorn Serpent can breathe only underwater.

Swift Current. As a bonus action on its turn, the Aquathorn Serpent can increase its movement speed by 20 feet until the end of its turn. This trait can be used once, and all expended uses are regained after a short or long rest.

Mystic Awareness. The Aquathorn serpent has advantage on saving throws against spells and other magical effects.

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 18 (2d10 + 7) piercing damage.

Tail Swipe. Melee Weapon Attack: +8 to hit, reach 15 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage. The Aquathorn Serpent can choose to hit all targets within a 10 ft. arc instead of a single target, potentially knocking them prone on a failed DC 16 Strength saving throw.

Thorned Coil. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 20 (3d8 + 7) piercing damage, and the target is grappled (escape DC 16). Until this grapple ends, the creature is restrained, and the Aquathorn Serpent can't constrict another target.

Aqua Spear (Recharge 5-6): The Aquathorn Serpent can magically launch a spear of water at one target it can see within 60 feet. The target must make a DC 15 Dexterity saving throw, taking 16 (3d10) piercing damage on a failed save, or half as much damage on a successful one. This attack ignores half cover and three-quarters cover.

Whirlpool Trap (Recharge 6): The Aquathorn Serpent can create a 20-foot-radius whirlpool centered on a point it can see within 100 feet. The whirlpool lasts for 1 minute and pulls creatures towards its center. Creatures within the whirlpool's area when it is cast, or that enter the area for the first time on a turn, must succeed on a DC 16 Strength saving throw or be pulled 10 feet towards the center and take 9 (2d8) bludgeoning damage. Creatures at the center of the whirlpool are restrained. The creature can choose to end the whirlpool early as a bonus action.