Ancient Remorhaz

Heated Body. A creature that touches the remorhaz or hits it with a melee attack while within 5 feet of it takes 14 (4d6) fire damage.

Bite. Melee Weapon Attack: +15 to hit, reach 5 ft., one target. Hit: 58 (9d10 + 9) piercing damage plus 14 (4d6) fire damage. If the target is a creature, it is grappled (escape DC 19). Until this grapple ends, the target is restrained, and the remorhaz can't bite another target.

Swallow. The remorhaz makes one bite attack against a Large or smaller creature it is grappling. If the attack hits, that creature takes the bite's damage and 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 remorhaz, and it takes 28 (8d6) acid damage at the start of each of the remorhaz's turns

  If the remorhaz takes 40 damage or more on a single turn from a creature inside it, the remorhaz must succeed on a DC 17 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 remorhaz. If the remorhaz dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 15 feet of movement, exiting prone.

Burst Forth (Recharges after a Short or Long Rest). As a bonus action, the remorhaz breaks through solid ground or wall, showering the area with debris. Each creature within 20 feet of the remorhaz must succeed on a DC 23 Strength saving throw, taking 33 (7d6 + 9) bludgeoning damage and is knocked prone on a failed save, or half as much damage and isn't knocked prone on a successful one.