Shoggoth

Anaerobic Nature. The shoggoth doesn't require air.

Absorb Flesh. When the shoggoth kills a creature while within 15 feet of it, the creature's body is absorbed into the shoggoth's. The creature can be restored to life only by means of a true resurrection or a wish spell.

Amorphous. The shoggoth can move through a space as narrow as 1 foot wide without squeezing.

Hideous Cacophony. The shoggoth's many mouths constantly emit whistles, fluting, and other high-pitched noises. It has disadvantage on Dexterity (Stealth) checks made to be unheard. Each creature that starts its turn within 60 feet of the shoggoth and that can hear it must make a DC 19 Wisdom saving throw or be disoriented until the start of its next turn. A disoriented creature is incapacitated, and when it moves, it moves in a random direction.

Keen Hearing and Smell. The shoggoth has advantage on Wisdom (Perception) checks that rely on hearing or smell.

Limited Mutability. Any spell or effect that would alter the shoggoth's form alters it for only 1 round. Afterward, the shoggoth returns to its amorphous blob form.

Multiattack. The shoggoth makes four Slam attacks. It can replace two Slam attacks with a use of Crush.

Slam. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 30 (4d10 + 8) bludgeoning damage, and the target is grappled (escape DC 18) if it is a Large or smaller creature.

Crush. The shoggoth crushes up to two creatures it is grappling by rolling them beneath its bulk. Each target must succeed on a DC 19 Strength saving throw or take 30 (4d10 + 8) bludgeoning damage, be unable to breathe, and be restrained until the grapple ends. If the shoggoth moves, a creature beneath it is no longer restrained and is able to breathe, but it remains grappled.