Multiattack

The drake makes one bite attack and one claw attack. If both attacks hit the same target, the drake can use its Deathroll on the target.

Bite

Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 8 (1d8 + 4) piercing damage.

Claw

Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) slashing damage.

Deathroll

The kelp drake latches onto a Medium or smaller creature it can see within 5 feet of it and rolls itself and the target. The target must make a DC 13 Constitution saving throw. On a failure, the creature takes 7 (2d6) slashing damage and is stunned until the end of its next turn. On a success, the creature takes half the damage and isn't stunned. The kelp drake can use this action only if both itself and the target are immersed in water.

Binding Bile (Recharge 6)

The drake forcibly vomits a long line of bile-coated kelp that unravels in a 30-foot-long, 5-foot-wide line. Each target in the area must make a DC 13 Dexterity saving throw. On a failure, a creature takes 14 (4d6) acid damage and is restrained by kelp for 1 minute. On a success, a creature takes half the damage and isn't restrained. A creature, including the target, can take its action to remove the kelp by succeeding on a DC 13 Strength check. Alternatively, the kelp can be attacked and destroyed (AC 10; hp 3; immunity to bludgeoning, poison, and psychic damage).