Constellation Whale

Air-breathing Megafauna. Constellation Whales are air-breathing, but can spend up to 6 hours underwater without needing to surface.

Arcane Predator. Constellation Whales sense distortions in weave, are actively searching for its sources and will immediately attack any creature casting a spell or wielding a magic item, as well as magical objects or vehicles. When fighting against such a target, Constellation Whales get the following traits:

• Anti-magic Constellation. Creatures, affected by the Mesmerizing Stars trait make any spell attack rolls and concentration checks with disadvantage for 1d4 rounds after they are no longer charmed by the effect.
• Eldritch Rage. When the Constellation Whale is hit by a spell, in its next turn it can add 2d12 points of damage to the damage roll against the creature that casted the spell. The effect targets any number of creatures casting inbetween Constellation Whale's turns.

Lone Hunter. Constellation Whales get advantage on attack rolls and saving throws while there is no other Constellation Whale in 2 mile radius.

Mesmerizing Stars. Constellation Whales have spots throughout their body, pulsating in mezmerizing patterns. Any creature that can see the Whale must make a DC 18 Wisdom saving throw or become charmed for 1d4 rounds.

Multiattack. The Constellation Whale can use its Echolocation. It then makes two attacks: one with its bite, and one with its tail. It can use its Swallow instead of its bite.

Echolocation. The Constellation Whale makes a resounding scream, making it able to determine location of any creatures within 100 ft. radius.

Tail Slam. Melee Weapon Attack: +9 to hit, reach 30 ft., 1 target. Hit: 40 (8d8 + 8) [bludgeoning] damage. 

Bite. Melee Weapon Attack: +10 to hit, reach 20 ft., one target. Hit: 36 (4d12 + 10) piercing damage. If the target is a creature, it is grappled (escape DC 18). Until this grapple ends, the target is restrained, and the Constellation Whale can’t bite another target.

Swallow. The Constellation Whale makes one bite attack against a Large or smaller creature it is grappling. If the attack hits, the target takes the bite’s damage, the target 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 Constellation Whale, is unable to cast any spells and it takes 14 (4d6) acid damage at the start of each of the Whale’s turns.

If the Constellation Whale takes 35 damage or more on a single turn from a creature inside it, the Constellation Whale must succeed on a DC 20 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 Constellation Whale. If the Whale dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement.