Freedom of Movement: The whale 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.
Seige Monster: The kraken deals double damage to objects and structures.
Multiattack:
The whale makes three air blast attacks each of which it can replace with one use of its tail attack or a Balleen of Lightning attack
Song of Storms:
The whale sings a magical melody. Every humanoid and giant within 300 ft. of the whale that can hear the song must succeed on a DC 11 Wisdom saving throw or be Charmed until the song ends. The whale must take a Bonus Action on its subsequent turns to continue singing. It can stop singing at any time. The song ends if the harpy is Incapacitated.
While Charmed by the whale a target is Incapacitated and ignores the songs of other whales. If the Charmed target is more than 5 ft. away from the whale it must move on its turn toward the whale by the most direct route. It doesn't avoid Opportunity Attacks but before moving into damaging terrain such as lava or a pit and whenever it takes damage from a source other than the whale a target can repeat the saving throw. A creature can also repeat the saving throw at the end of each of its turns. If a creature's saving throw is successful the effect ends on it.
A target that successfully saves is immune to this whale's song for the next 24 hours.
Air Blast:
One Large or smaller object within 90ft of the whale is targeted by a magical blast of air throwing them up to 60 feet in a direction of the whale's choosing 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.
Frightful Presence:
Each creature of the whale's choice within 120 feet of it and aware of it must succeed on a DC 17 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns with disadvantage if the whale is within line of sight ending the effect on itself on a success. If a creature̢s saving throw is successful or the effect ends for it the creature is immune to the whale's Frightful Presence for the next 24 hours.
Tail:
Melee Weapon Attack: +19 to hit reach 20 ft. one target. Hit: 24 (4d6 + 10) bludgeoning damage. If the target is a creature it must succeed on a DC 20 Strength saving throw or be knocked prone.
Balleen of Lightning:
Melee Weapon Attack: +17 to hit reach 10 ft. all creatures within a 15ft diameter are targeted. Hit: 23 (3d8 + 10) lightning damage. If the target is a creature it is grappled/stunned (escape DC 20). Until this grapple/stun ends the target is restrained.
Swallow:
If the target is a Large or smaller creature grappled by the storm whale 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 whale and it takes 42 (12d6) lightning damage at the start of each of the whale's turns. If the whale takes 50 damage or more on a single turn from a creature inside it the whale 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 storm whale. If the storm whale dies a swallowed creature is no longer restrained by it and can escape from the corpse using 30 feet of movement exiting prone.