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

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.

Skill: Perception

Skill: Stealth

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.