Actions

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.

Legendary Actions