This monster appears in the Dungeons & Dragons Player's Handbook 2024.
Traits
Compression. The octopus can move through a space as narrow as 1 inch without spending extra movement to do so.
Water Breathing. The octopus can breathe only underwater.
Actions
Tentacles. Melee Attack Roll: +4, reach 5 ft. Hit: 1 Bludgeoning damage.
Reactions
Ink Cloud (1/Day). 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 Heavily Obscured for 1 minute or until a strong current or similar effect disperses the ink.