Valtameri

Amphibious. The Valtameri can breathe in and out of water. 

Underwater Camouflage. The Valtameri has advantage on Dexterity (Stealth) checks made while underwater.

False Appearance: While the Valtameri remains motionless, it is indistinguishable from a normal coral.

Grasping Tentacles: The Valtameri can have up to 20 tentacles at a time. Each tentacle can be attacked (AC 20; 10 hit points; immunity to poison and psychic damage). Destroying a tentacle deals 1D12 + 4  piercing damage. A tentacle can also be broken if a creature takes an action and succeeds on a DC 17 Strength check against it.

Suction Climb: The Valtameri can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Non-newtonian musculature: When Hit with an attack that deals bludgeoning damage (non-magical and magical), The Valtameri's AC increases by 2 each time (will stack). But its swim speed decreases by 10 ft for one round due to the stiffening of its muscle structure.

Multiattack: The Valtameri makes four attacks with its tentacles, uses Reel, and makes one Attack with its bite.

Bite: Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 22 (4d8 + 4) piercing damage..

Reel. The Valtameri pulls each creature Grappled by it up to 25 ft. straight toward it.

Tentacles. Melee Weapon Attack: +5 to hit, reach 15 ft., one target. Hit: (2d6 + 3) bludgeoning damage. If the target is a creature, it is grappled (escape DC 16). Until this grapple ends, the target is restrained, and the Valtameri can’t use its tentacles on another target

Ink Cloud (Recharges after a Short rest). A 20-foot-radius cloud of ink extends all around the Valtameri 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 Valtameri can use the Dash action as a bonus action.