Avarnian Kraken

Amphibious. The Kraken can breathe air and water.

Legendary Resistance (3/Day). If the Kraken fails a saving throw, she can choose to succeed instead. 

Freedom of Movement. The Kraken ignores difficult terrain, and magical effects can't reduce her speed or cause her to be restrained. She can also use 5 feet of movement to escape from non-magical restraints and being grappled. 

Siege Monster. The Kraken deals double damage to objects and structures.

Regeneration. If the Kraken takes 40 or more damage in a single turn, one of its tentacles falls off. Once a tentacle is cut off, it will completely regrow under (1d8) days. 

Multiattack. The Kraken makes three tentacle attacks, each of which she can replace with one use of Fling.

Tentacle. Melee Weapon Attack: +17 to hit, reach 60 ft., one target. Hit: 34 (6d8 + 10) bludgeoning damage, and the target is grappled (escape DC 18). Until this grapple ends, the target is restrained. The Kraken has sixteen tentacles, including her clawed tentacles, each of which can grapple one target.

Claw Tentacle. Melee Weapon Attack: +17 to hit, reach 80 ft., one target. Hit: 53 (12d8 + 10) piercing damage, and the target is grappled (escape DC 21). Until this grapple ends, the target is restrained. The Kraken has two clawed tentacles, each of which can grapple one target.

Fling. One Large or smaller object held or creature grappled by the Kraken is thrown up to 60 feet in a random direction and knocked prone. If a thrown target strikes a solid surface, the target takes 3 (1d6) bludgeoning damage for every 10 feet it was thrown. If the target is thrown at another creature, that creature must succeed on a DC 18 Dexterity saving throw or take the same damage and be knocked prone.

Tsunami (Recharge 5 - 6). The Kraken conjures up a gigantic wave of water, equal to a 9th level Tsunami spell. 

Titan Whirlpool (1/day). The Kraken sinks down to the bottom of the ocean, turning upside down with her tentacles spread. She opens her gigantic mouth and begins to suck in everything above her, creating a massive whirlpool, which lasts until the end of the following round. The whirlpool forms a vortex that is 20 feet wide at the base, up to 120 feet wide at the top, and 100 feet tall. Any creature or object in the water and within 25 feet of the vortex is pulled 10 feet toward it. A creature can swim away from the vortex by making a DC 23 Athletics check. When a creature enters the vortex for the first time on a turn or starts its turn there, it must make a Strength saving throw. On a failed save, the creature takes (6d8) bludgeoning damage and is caught in the vortex until the end of the next round. On a successful save, the creature takes half damage, and isn't caught in the vortex. A creature caught in the vortex can use its action to try to swim away from the vortex as described above, but has disadvantage on the Strength (Athletics) check to do so. The first time each turn that an object enters the vortex, the object takes (6d8) bludgeoning damage, this damage occurs each round. A creature or object that is caught in the vortex descends 20 feet at the end of each of their turn, and the Kraken's turn. When a creature or an object descends to the bottom of the vortex, they are sucked into the Kraken's mouth, taking (38d6) piercing damage. Once the whirlpool has ended, the Kraken closes her mouth, swallowing all creatures inside. A swallowed creature is blinded and restrained, has full coverage of attacks and other effects outside the Kraken, and takes (12d6) acid damage plus (6d4) piercing damage at the end of each of the Kraken's turns. If the Kraken dies, all creatures can escape from the corpse using 20 feet of movement. 

The Kraken can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Kraken regains spent legendary actions at the start of her turn.

Tentacle Attack or Fling. The Kraken makes one tentacle attack or uses her Fling.

Camouflage (Costs 2 Actions). The Kraken changes her coloration and the texture of her skin to blend in with her surroundings. This lasts until the start of the Kraken's second turn, or until she chooses to end the camouflage as a bonus action. A creature attempting to locate the Kraken must succeed on a DC 21 Perception check. This check has advantage if the Kraken moves more than 10 feet in any direction, or attacks. While camouflaged, attacks have disadvantage against the Kraken, unless a creature has succeeded their Perception check. 

Ink Cloud (Costs 3 Actions). While underwater, the Kraken expels an ink cloud in a 240-foot radius. The cloud spreads around corners, and that area is heavily obscured to creatures other than the Kraken. A strong current disperses the cloud, which otherwise disappears at the end of the Kraken's next turn.