Hold Breath. While out of water, the octopus can hold its breath for 30 minutes.

Underwater Camouflage. The octopus has advantage on Dexterity (Stealth) checks made while underwater.

Water Breathing. The octopus can breathe only underwater.

Tentacles. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 1 bludgeoning damage, and the target is grappled (escape DC 10). Until this grapple ends, the octopus can't use its tentacles on another target.

Ink Cloud (Recharges after a Short or Long Rest). A 5-foot-radius cloud of ink extends all around the octopus if it is underwater. The area is heavily obscured for 1 minute, although a significant current can disperse the ink. After releasing the ink, the octopus can use the Dash action as a bonus action.