Aquanyx

Nocturnal. This creature sleeps during the day or stays in dark areas while the sun is out.

Amphibious. This creature is able to breathe air and water.

Deep Hunter. This creature hunts by luring creatures using lights to its mouth.

Superior Hearing. This creature is able to hear things despite them attempting to hide themselves. Creatures attempting to hide don't add anything but their normal modifiers

Multiattack. The Aquanyx can use its Frightful Presence. It then makes five attacks: one with its bite, two with its claws, one with its horns, and one with its tail. It can use its Swallow instead of its bite.

Bite. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 32 (4d12 + 6) piercing damage. If the target is a creature, it is grappled (escape DC 20). Until this grapple ends, the target is restrained, and the Aquanyx can't bite another target.

Claw. Melee Weapon Attack: +16 to hit, reach 15ft., one target. Hit: 24 (4d8 + 6) slashing damage.

Tail. Melee Weapon Attack: +16 to hit, reach 40ft., one target. Hit: 20 (4d6 + 6) bludgeoning damage. If the target is a creature, it must succeed on a DC 20 Strength saving throw or be knocked prone.

Frightful Presence. Each creature of the Aquanyx's choice within 120 feet of it and aware of it must succeed on a DC 20 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 Aquanyx is within line of sight, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the Aquanyx's Frightful Presence for the next 24 hours.

Swallow. The Aquanyx 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 Aquanyx, and it takes 44 (12d6) acid damage at the start of each of the Aquanyx's turns.

If the Aquanyx takes 50 damage or more on a single turn from a creature inside it, the Aquanyx 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 Aquanyx. If the Aquanyx dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.

The Aquanyx can take 3 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 Aquanyx regains spent legendary actions at the start of its turn.

Attack. The Aquanyx makes one claw attack or tail attack.

Move. The Aquanyx moves up to half its speed.

Chomp (Costs 2 Actions). The Aquanyx makes one bite attack or uses its Swallow.