Amphibious. The swarm can breathe air and water.

Freedom of Movements. The swarm ignores difficult terrain, and magical effects can't reduce there speed or cause them to be restrained. they can spend 5 feet of movement to escape from nonmagical restraints or being grappled.

Siege Monsters. The swarm deals double damage to objects and structures.

Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a gargantuan tarrasque. The swarm gain temporary hit points. 

Multiattacks. The swarm makes thirty tentacle attacks or make ten bites attacks, each of which they can replace with one use of Flings.

Bites. Melee Weapon Attack: +17 to hit, reach 5 ft., one target. Hit: 23 (3d8 + 10) piercing damage. If the target is a Large or smaller creature grappled by the swarm, that creature is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the swarm, and it takes 42 (12d6) acid damage at the start of each of the kraken's turns.

If the swarm takes 50 damage or more on a single turn from a creature inside it, the swarm must succeed on a DC 25 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the swarm. If the swarm dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 15 feet of movement, exiting prone.

Tentacles. Melee Weapon Attack: +17 to hit, reach 30 ft., one target. Hit: 100 (30d6 + 10) bludgeoning damage, and the target is grappled (escape DC 18). Until this grapple ends, the target is restrained. The swarm has hunderd tentacles, each of which can grapple one target.

Flings. all Large or smaller object held or creature grappled by the swarm 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.

Lightning Storms. The kraken magically creates three bolts of lightning, each of which can strike a target the swarm can see within 1200 feet of it. A target must make a DC 26 Dexterity saving throw, taking 220 (40d10) lightning damage on a failed save, or half as much damage on a successful one.

The swarm can take 30 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 swarm regains spent legendary actions at the start of there turn.

Tentacles Attack or Flings (Costs 10 Actions). The swarm makes ten tentacles attack or uses there Flings.

Lightning Storms (Costs 20 Actions). The storm uses Lightning Storms.

Ink Clouds (Costs 3 Actions). While underwater, the swarm expels an ink cloud in a 600-foot radius. The cloud spreads around corners, and that area is heavily obscured to creatures other than the swarm. Each creature other than the swarm that ends its turn there must succeed on a DC 46 Constitution saving throw, taking 160 (30d10) poison damage on a failed save, or half as much damage on a successful one. A strong current disperses the cloud, which otherwise disappears at the end of the swarm's next turn.