Corragula the Polluted Abomination

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

Diseased Body. A creature that touches Corragula or hits it with a melee attack while within 5 feet of it makes a DC 13 Constitution saving throw against being diseased.

Corrosive Form. A creature that touches Corragula or hits it with a melee attack while within 5 feet of it takes 4 (1d8) acid damage. Any nonmagical weapon made of metal or wood that hits Corragula corrodes. After dealing damage, the weapon takes a permanent and cumulative −1 penalty to damage rolls. If its penalty drops to −5, the weapon is destroyed.

Nonmagical ammunition made of metal or wood that hits Corragula is destroyed after dealing damage.

Corragula can eat through 2-inch-thick, nonmagical wood or metal in 1 round.

Spider Climb. Corragula 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 (2d6 + 3) bludgeoning damage plus 18 (4d8) acid damage. The targeted individual also makes a DC 13 Constitution saving throw against being diseased. In addition, nonmagical armor worn by the target is partly dissolved and takes a permanent and cumulative −1 penalty to the AC it offers. The armor is destroyed if the penalty reduces its AC to 10.

Projectile Secretion. Ranged Attack: +3 to hit, reach 15 ft., one target. Hit: 21 (6d8) acid damage and makes a DC 13 Constitution saving throw against being diseased. Can only be used every other turn. In addition, nonmagical armor worn by the target is partly dissolved and takes a permanent and cumulative −1 penalty to the AC it offers. The armor is destroyed if the penalty reduces its AC to 10.

Advanced Mitosis. When Corragula is subjected to lightning or slashing damage, it creates two black puddings from the damaged area if it has at least 10 hit points. Each new pudding has hit points equal to half of Corragula's, rounded down. New puddings are one size smaller than Corragula. 

Hard Coating. When Corragula is subjected to piercing damage, it creates a hardened coating made of refuse increasing it's AC by 2 for the next 2 rounds.