Grindylow

Mimicry. The grindylow can mimic humanoid voices. A creature that hears the sounds can tell they are imitations with a successful DC 13 Wisdom (Insight) check.

Slippery. The grindylow has advantage on ability checks and saving throws made to escape a grapple.

Water Breathing. The grindylow can breathe only underwater.

Multiattack. The grindylow makes two attacks: one with its bite and one with its claws.

Bite. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) piercing damage.

Claws. Melee Weapon Attack: +3 to hit, reach 10 ft., one target. Hit: 8 (2d6 + 1) slashing damage and the target is grappled (escape DC 13). Until this grapple ends, the target is restrained, and the grindylow can't use its claws on another target.

Ink Cloud (Recharges after a Short or Long Rest). A 20-foot-radius cloud of ink extends all around the grindylow if it is underwater. The area is heavily obscured for 1 minute, although a significant current can disperse the ink. After releasing the ink, the grindylow can use the Dash action as a bonus action.