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

Water Breathing. The octopus can breathe  underwater.

Tentacles. Yuh whips out a few tentacles to injure/poison the target.

Tentacle Melee Attack. Melee Weapon Attack: +7 to hit, reach 5 ft., 1 target. Hit: 1 (1d6 + 7) [poison] damage.

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.