Underwater Camouflage. The Reef Reaver has advantage on Dexterity (Stealth) checks made while underwater.
Immutable Form. The Reef Reaver is immune to any spell or effect that would alter its form.
Command Quippers (recharge 6). The Reef Reaver may summon a Swarm of Quippers to attack its foes. There may not be more than two swarms active at a time. Roll 1d6 at the top of its turn to regain use of this ability.

Multiattack. The Reef Reaver makes two slam attacks, an octohand and fling attack, or a water jet and stomp attack.
Slam. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 14 (2d8 + 5) bludgeoning damage. If target is grappled by the octopus hand, the Reef Reaver has advantage on the attack and deals an additional 3 (1d6) bludgeoning damage.
Stomp. Melee Weapon Attack: +7 to hit, reach 10 ft., one prone. Hit: 10 (2d6 + 5) bludgeoning damage. On a hit, the target must make a DC 16 Dexterity saving throw or be incapacitated until the start of the Reef Reaver's next turn.
Fling. One Medium or smaller object held, or creature grappled by the Reef Reaver's Octohand, is thrown up to 40 feet in a random direction and knocked prone. If a thrown target strikes a solid surface, the target takes 3 (1d4) bludgeoning damage for every 10 feet it was thrown. It the target is thrown at another creature, that creature must succeed on a DC 18 Dexterity saving throw or take the same damage and be knocked prone.
Water Jet. The Reef Reaver magically shoots water in a 60-foot line that is 5 feet wide. Each creature in that line must make a DC 16 Dexterity saving throw. On a failure, a target takes 15 (4d6) bludgeoning damage and, if it is Huge or smaller, is pushed up to 15 feet away from the Reef Reaver and knocked prone. On a success, a target takes half the bludgeoning damage, but is neither pushed nor knocked prone.
Octohand. Melee Weapon Attack: +6 to hit, reach 10ft, one target. One a hit, the target it grappled. Until this grapple ends, the target is restrained. On each turn the target may use their action to make a DC 16 Strength saving throw to break the grapple.

Ink Jet (2 uses, recharge 6). Upon being attacked, the Reef Reaver may use the ink of the octopus which makes up its left hand (Octohand) to give a -3 to the attack roll; this must be done before damage is rolled/dealt.  This cannot be used if it is grappling someone in this hand.  Roll 1d6 at the top of its turn to regain a single expended use.