Crochemoth

Hold Breath. The crochemoth can hold its breath for up to 30 minutes.

Multiattack. The Crochemoth makes 2 attacks with its claws and 1 with its bite. If it starts its turn grappling a creature with its bite, it uses Death Roll instead of its normal attacks.

Claw. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 16 (3d6 + 6) slashing damage. 

Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 25 (3d12 + 6) piercing damage and the target is grappled (escape DC 18). Until this grapple ends, the target is restrained, and the Crochemoth can't bite another target.

Tail. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage and the target must make a DC 18 Strength saving throw or be knocked prone.

Death Roll. If the crochemoth is grappling a Large or smaller creature with its jaws, it drops prone with the grappled creature and begins a vicious death roll, moving 15 feet to its right or left. The grappled creature automatically takes 19 (2d12+6) piercing damage and 23 (3d10+6) bludeoning damage and an again at the start of the Crochemoth's turns as the Death Roll continues. Additionally, the grappled creature has disadvantage on checks to break this grapple.

While maintaining the Death Roll, the Crochemoth moves 15 feet in the same direction as it began. If the Crochemoth moves into the space of another creature or if another creature gets within 5 feet of it while Death Rolling, that creature must make a DC 18 Dexterity save or be pushed to the nearest unocupied space 5 feet away from the Crochemoth and knocked prone. A creature that succeeds this save is not knocked prone.

Tail Swipe. When the crochemoth can make an opportunity attack, it can make a tail attack instead of its claw or bite.