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

Aquatic. The slime can only survive for a few hours out of water.

False Appearance. While the slime is underwater, it is indistinguishable from the mud it nests in, though it will emit foul-smelling bubbles.

Grapple. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 9 (1d12 + 3) poison damage. Until this grapple ends, the creature is restrained, and the slime can't grapple another target.

Each turn you start grappled, you take 1d12 poison damage (per slime grappling you). If you take 10 or more damage from this poison in a single turn, you are Poisoned.

You can break a grapple by wriggling (win a contest of Dexterity (Acrobatics) vs. Strength (Athletics)) or by force (Strength (Athletics) for both combatants).

Contagion. When a slime is subjected to bludgeoning or slashing damage, it releases a cloud of toxic vapor.  Anyone within 5 ft. must pass a Constitution save (DC 12) or become Incapacitated.   The victim may attempt the save again at the end of each of their turns.

Entrap.  If stepped on while in its nest, the slime will ooze aside, sucking its victim down several feet into the mud.  The victim must pass a Dexterity save (DC 15) or become restrained.