Bonepit Lurker

Bone Armor. A creature that touches the lurker or hits it with a melee attack while within 5 feet of it takes 4  (1d8) piercing damage

Legendary Resistance (3/Day). If Strahd fails a saving throw, he can choose to succeed instead.

Stone Camouflage. The lurker has advantage on Dexterity (Stealth) checks made to hide in rocky terrain.

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

Tunneler. The worm can burrow through solid rock at half its burrow speed and leaves a 10-foot-diameter tunnel in its wake.

Multiattack. The lurker makes two attacks: one with its bite and one with its slam.

Bite. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 22 (3d8 + 9) piercing damage. If the target is a Large or smaller creature, it must succeed on a DC 19 Dexterity saving throw or be grappled and restrained by the lurker.

Glue Spit (1d6)(Recharge 5–6).. The lurker spits acid in a 40-foot line that is 5 feet wide. Each creature in that line must make a DC 19 Dexterity saving throw. on a failed save the creature takes 10 (3d6)  acid damage and is restrained by a thick, glue like substance (escape DC 19). On a success they take half as much damage and are not restrained.

Swallow. The lurker makes one bite attack against a Medium or smaller target it is grappling. If the attack hits, the target is also swallowed, and the grapple ends. While swallowed, the target is blinded and restrained, it has total cover against attacks and other effects outside the lurker, and it takes 21 (6d6) acid damage at the start of each of the lurker’s turns. A lurker can have only one creature swallowed at a time.

f the lurker takes 30 damage or more on a single turn from the swallowed creature, the lurker must succeed on a DC 14 Constitution saving throw at the end of that turn or regurgitate the creature, which falls prone in a space within 10 feet of the lurker. If the lurker dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 15 feet of movement, exiting prone

Reactive Strike. Other creatures provoke an opportunity attack from the lurker when they enter within 10-feet

The lurker 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 lurker regains spent legendary actions at the start of its turn.

Move. The lurker moves up to its speed without provoking opportunity attacks

Bite (Costs 2 Actions). The lurker makes one bite attack

Slam (Costs 3 Actions). The lurker stretches upwards and then tips over crashing onto everything in its wake. Each creature in a line 40-foot long and 10-foot wide must make a DC 19 Dexterity saving throw, taking 14 (4d6) bludgeoning damage plus 14 (4d6) piercing damage on a failed save, or half as much damage on a successful one.