Bigooblin

False Appearance. While the Bigooblin remains motionless, it is indistinguishable from a large puddle of poisonous sludge.

Rotting Stench. Any creature that starts its turn within 15 feet of the Bigooblin must succeed on a DC 16 Constitution saving throw or be poisoned until the start of its next turn.

Amorphous Body. The Bigooblin can move through a space as narrow as 1 inch wide without squeezing, provided it isn’t carrying or engulfing another creature.

Toxic Body. A creature that touches the Bigooblin or hits it with a melee attack while within 5 feet of it takes 17 (5d6) poison damage. A creature that enters the Bigooblin’s space for the first time on a turn or starts its turn there takes the same damage.

Multiattack. The Bigooblin makes three Slam attacks or one Slam attack and the Get in my belly! attack.

Slam. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 19 (3d8 + 6) bludgeoning damage.

Get in my belly! The Bigooblin moves up to its speed. While doing so, it can enter the spaces of Large or smaller creatures. Whenever it enters a creature’s space, that creature must make a DC 16 Dexterity saving throw. On a successful save, the creature can choose to be pushed 5 feet away from the Bigooblin. On a failed save, the creature is engulfed. An engulfed creature is restrained, unable to breathe, and takes 21 (6d6) poison damage at the start of each of the Bigooblin’s turns. When the Bigooblin moves, the engulfed creature moves with it. The Bigooblin can have up to three creatures engulfed at a time.

An engulfed creature can use its action to make a DC 16 Strength check, escaping on a success and appearing in a space of its choice within 5 feet of the Bigooblin. If the Bigooblin dies, an engulfed creature is no longer restrained by it.

Splatter. When the Bigooblin takes damage from a melee attack by a creature within 10 feet of it, it can splash toxic sludge onto that creature. The attacker must succeed on a DC 16 Dexterity saving throw or take 10 (3d6) poison damage.