Bakekujira

Disgorge Fish. As a bonus action, the whale can disgorge an undead school of fish which appears in an unoccupied space within 10 feet of it. The disgorged school uses the statistics of a swarm of quippers, except that it is a Medium swarm of Tiny undead which does not need to breathe and has a flying speed of 40 feet and can hover.  The undead school of fish acts on its own initiative count. After a school of fish is disgorged, roll a d6. On a roll of 1, the whale runs out of fish to disgorge and loses this trait. If the whale still has this trait when it dies, 1d4 schools erupt from its corpse at the start of its next turn. These schools act on their own initiative count.

Echolocation. The whale can’t use its blindsight while deafened.

Keen Hearing. The whale has advantage on Wisdom (Perception) checks that rely on hearing.

Multiattack. The whale makes two attacks: one with its bite and one with its tail.

Bite. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 21 (3d8 + 8) piercing damage. If the target is a Large or smaller creature, it must succeed on a DC 14 Dexterity saving throw or be swallowed by the whale. A swallowed creature has total cover against attacks and other effects outside the whale, and it takes 3 (1d6) necrotic damage at the start of each of the whale’s turns. If the whale takes 30 damage or more on a single turn from a creature inside it, the whale must succeed on a DC 16 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 whale. If the whale dies, a swallowed creature can escape from the corpse by using 20 feet of movement, exiting prone.

Tail. Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 18 (3d6 + 8) bludgeoning damage, or 37 (6d6 + 16) bludgeoning damage if the target is an object.

Shadow Plume (Recharge 5–6). The whale exhales a cloud of darkness from its blowhole in a 30-foot cone. The cloud spreads around corners, and that area is heavily obscured to creatures other than the whale. Each creature in the area when the cloud appears or that that ends its turn there must succeed on a DC 14 Constitution saving throw, taking 55 (10d10) necrotic damage and becoming frightened for 1 minute on a failed save, or half as much damage withing being frightened on a successful one. A frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. A strong current or breeze (at least 10 miles per hour) disperses the cloud, which otherwise disappears at the end of the whale's next turn.