Myrtle Slime

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

Corrode Metal. Any non-magical weapon made of metal that hits the slime 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. Non-magical ammunition made of metal that hits the slime is destroyed after dealing damage. The slime can eat through 2-inch-thick, non-magical metal in 1 round.

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

False Appearance. While the slime remains motionless, it is indistinguishable from a common moss.

Multiattack. The myrtle slime can make one Pseudopod attack followed by an Engulf if successful.

Pseudopod. Melee Weapon Attack: +5 to hit, reach 5 ft., 1 target. Hit: 9 (2d6 + 2) bludgeoning damage. 

Engulf. Upon a successful melee attack, the slime can automatically grapple its victim as a bonus action, doing 2 (1d4) acid damage per round until dead or removed. It can only engulf one creature its size or smaller. Attacks against it are at disadvantage to avoid hitting its prey.

Split. When a slime that is Medium or larger is subjected to slashing damage, it splits into two new slimes if it has at least 10 hitpoints. Each new slime has hitpoints equal to half the original slime’s, rounded down. The new slimes are one size smaller than the original slime.