Brown Pudding

Amorphous. The pudding can move through a space as narrow as 1 inch wide without squeezing.

False Appearance. While the pudding remains motionless, it is indistinguishable from a giant turd.

Floater. The pudding's speed doubles when it is in water and can only move across its surface.

Flushable. The pudding takes 1d10 acid damage whenever it is struck by or ends its turn in running water. 

Spider Climb. The pudding can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Pseudopod. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) bludgeoning damage plus 18 (4d8) poison damage.

Explosive Diarrhea. A spray of fecal matter bursts out from the brown pudding. Each creature within 10 feet of the pudding must make a DC 10 Dexterity saving throw. On a failed save, a creature takes 2d8 poison damage and has disadvantage on any attack rolls until the start of the pudding's next turn. On a successful save, the creature takes half as much damage.

In addition, the pudding takes half of the damage rolled as necrotic damage a result of expelling its body mass.

Split. When a pudding that is Medium or larger is subjected to lightning or slashing damage, it splits into two new puddings if it has at least 10 hit points. Each new pudding has hit points equal to half the original pudding's, rounded down. New puddings are one size smaller than the original pudding.