Crocolith

Amphibious. The Crocolith can breath air and water.

Abyssal Nature. The Crocolith can swim in the River Styx without suffering any penalties for doing so.

Siege Monster. The Crocoltih deals double damage to objects and structures.

Multiattack. The Crocolith makes one Bite attack and two claw attacks. The Bite attack can be replaced with either a Tail attack, or a Fling action.

Bite. Melee Attack Roll: +11 to hit, reach 10 ft. Hit: 22 (3d10 + 7) Piercing damage. If the target is Medium or smaller, it has the Grappled condition (escape DC 15). While Grappled, the target has the Restrained condition. If the Crocolith is already grappling a creature in this way, the Crocolith can only target that creature with the Bite attack, which is made at advantage.

Claw. Melee Attack Roll: +11 to hit, reach 5 ft. Hit: 16 (2d6 + 7) Slashing damage.

 Tail. Melee Attack Roll: +11to hit, reach 15 ft. Hit: 11 Bludgeoning damage. The target must make a DC17 STR saving throw or be knocked prone.

Billious Spray (Recharge 5-6): +11 to hit; reach 30 ft line. Hit: 16 (8d10) Acid damage. DC17 Dex Save or half.

Fling. A large or smaller creature grappled by the Crocolith's Bite attack is thrown up to 60 feet in a straight line and knocked prone. The creature takes 1d6 Bludgeoning damage for every 10 feet thrown. If the creature is thrown at another creature, the target must make a DC17 DEX saving throw, or take the same damage and be knocked prone.

Crushing Grip. If creature grappled attempts to escape, roll a number of D4's equal to the difference between the creature's STR modifier and the Crocolith's. The grappled creature takes bludgeoning damage equal to the result.

Death Roll. If the Crocolith is dealt damage by a creature grappled by it, the Crocolith can roll up to half of its movement speed without provoking attacks of opportunity, and the grappled creature takes 2d8 bludgeoning damage.