Giant Octopus

Camouflage. The octopus has advantage on Stealth checks.

Water Breathing. The octopus breathes water and can hold its breath for 1 hour while in air.

Tentacles. Melee Weapon Attack: +5 to hit, reach 15 ft., one target. Hit: 8 (2d4+3) bludgeoning damage. If the target is a creature it is grappled (escape DC 13). Until this grapple ends the target is restrained and the octopus can't attack a different target with its tentacles.

Ink Cloud (1/Day). If underwater, the octopus exudes a cloud of ink in a 20-foot-radius sphere, extending around corners. The area is heavily obscured for 1 minute unless dispersed by a strong current.