Crypt Lurker

Aberrant Mind. The lurker has advantage on Charisma, Intelligence and Wisdom saving throws.

Multiattack. The lurker can make two attacks of it choice.

Slam. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 11 (2d8 + 5) bludgeoning damage. 

Erase Existence. The lurker targets a creature it can see within 60 feet of it, forcing it to make a DC 15 Wisdom saving throw. On a failed save, the lurker becomes invisible to the creature. While invisible, the lurker cannot be tracked or detected in any way by the creature. The lurker becomes visible to the creature again if it attacks a creature or forces one to make a saving throw.

Dead End. The lurker targets a creature it can see within 60 feet of it, forcing it to make a DC 15 Wisdom saving throw. On a failed save, the creature perceives itself to be stuck in a room with the lurker. For 1 minute, the creature's movement speed is reduced to 0. It can reroll it's saving throw at the end of each of its turns, ending the effect on a success.

Meld Into Stone. As a bonus action, the lurker can step into a stone object or surface large enough to fully contain its body within 5 feet of it, melding with the stone for the duration. Nothing of its presence remains visible or otherwise detectable by non-magical senses. While merged with the stone, the lurker can't see what occurs outside it, and has disadvantage on any Wisdom (Perception) checks it makes to hear sounds outside it. The lurker can spend 5 feet of its movement to leave the stone. It otherwise can't move. The stone's complete destruction expels the lurker and deals 20 bludgeoning damage to it. If expelled, the lurker falls prone in an unoccupied space closest to where it first entered.

Lurking Horror. As a reaction to a creature moving to within 5 feet of it, the lurker can use its Dead End or Erase Existence actions, targeting the creature.