Hold Breath. While out of the 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.
Pack Magic (2nd level 2 spell)
Cantraps: Chill Touch, Eldritch Bast, Freinds
Spells: Create or destroy water, Hellish Rebuke, Armor of Agathas, Hold Person, Silence
Tentacle of the Deep
Gift of the Sea
Pact of the blade
Tentacles. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 1d4 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.
Tentacle Grasp: When you make a successful grapple the target is considered incompasitaed.