Huge monstrosity, any

Armor Class: 12 (natural armor)

Hit Points: 90 (12d12 + 12) 12d12+12

Speed: 0 ft , swim: 60 ft

STR

19 +4

DEX

10 +0

CON

13 +1

INT

12 +1

WIS

12 +1

CHA

10 +0

Skills: Arcana +3, Perception +3, Religion +3

Senses: darkvision 120 ft., passive Perception 13

Languages: Celestial, Common

Challenge Rating: 3

Ancient Carp by Christopher Burdett

Actions

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 21 (5d6 + 4) bludgeoning damage., and the target is grappled (escape DC 14). Until this grapple ends, the target is restrained, and the carp can't bite another target.
Swallow. The carp makes one bite attack against a medium or smaller target it is grappling. If the attack hits, the target is swallowed, and the grapple ends. The swallowed target is blinded and restrained, it has total cover against attacks and other effects outside the carp, and it takes 5 (2d4) acid damage at the start of each of the carp's turns. The carp can have only one target swallowed at a time. If the carp dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 5 feet of movement, exiting prone.