Black Star Kraken

Grapple. Instead of dealing damage on a tentacle attack, the black star kraken can instead grapple a target who is at least one size smaller than the kraken. The target must succeed a DC 20 strength saving throw or be thrown on their next turn.

Throw. If an item or creature is grappled by the black star kraken then it will throw them on its next turn. The thrown creature has to make a DC 19 Dexterity saving throw. On a failed save the thrown creature takes 4d8 bludgeoning damage and half as much on a successful save.

Freedom of Movement. The black star kraken ignores difficult terrain, and magical effects can't reduce its speed or cause it to be restrained. It can spend 5 feet of movement to escape from nonmagical restraints or being grappled.

Siege Monster. The black star kraken deals double damage to objects and structures.

Magic Resistance. The black star kraken has advantage on saving throws against spells and other magical effects.

Amphibious. The kraken can breathe air and water.

Multiattack. The black star kraken can make two attacks. Two tentacle attacks, two spiked tentacle attacks, or any tentacle and poison breath.

Terror of the seas. During the first round of combat the kraken makes a frightening screech and any creature in a 100 ft radius of it must make a DC 13 Charisma saving throw or be frightened for their next 3 turns.

Tentacle. Melee Weapon Attack: +7 to hit, reach 120 ft., 1 target. Hit: 30 (5d10 + 5) bludgeoning damage. 

Spiked tentacle. Melee Weapon Attack: +10 to hit, reach 150 ft., 1 target. Hit: 36 (5d12 + 6) piercing damage. 

Poison spray. RangedWeapon Attack: +7 to hit, range 80/460 ft., 7 target. Hit: 9 (2d8 + 1) poison damage.

The black star kraken can make 4 legendary actions at any time in the game.

Infernal power (Costs 2 Actions) instead of shooting a breath of poison, the kraken shoots out a breath of fire in a cone (80/500 ft). Any creature in the area of effect must make a DC 19 dexterity saving throw or take 4d8 fire damage. The area of effect will stay on fire for 7 turns.

Naval ram (Costs 1 Actions) the kraken can use up one of its legendary actions to ram any large item in the water causing the item to take 7d10 bludgeoning damage and any creature on the item to have to make a DC 17 Dexterity saving throw or be thrown from the item and take 2d8 bludgeoning damage.

Bite (Costs 1 Actions) the kraken can use one of its legendary actions to attack a boat or a large item with its beak causing the item to take 7d12 piercing damage. The item will take 3d12 damage per turn until the kraken takes 20 points of damage and let’s go.