Octopus

The monster can move through a space as narrow as 1 inch without expending extra movement to do so.

The monster can breathe only underwater.

. . If the target is a Medium or smaller creature, it has the Grappled condition (escape DC ) from all four tentacles.

Trigger: A creature ends its turn within 5 feet of the octopus while underwater. Response: The octopus releases ink that fills a 5-foot Cube centered on itself, and the octopus moves up to its Swim Speed. The Cube is heavilyobscured for 1 minute or until a strong current or similar effect disperses the ink.