Blood Frenzy. The sahuagin has advantage on melee attack rolls against any creature that doesn't have all its hit points.

Limited Amphibiousness. The sahuagin can breathe air and water, but it needs to be submerged at least once every 4 hours to avoid suffocating.

Shark Telepathy. The sahuagin can magically command any shark within 120 feet of it, using a limited telepathy.

Aquatic advantage: The sahuagin can make attacks of opportunity against enemies underwater

Multiattack. The sahuagin makes two melee attacks: one with its bite and one with its claws 

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) piercing damage.

Claws. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 14 (2d10 + 3) slashing damage.

Rage slam (Recharge 3). Whenever the Adacthys is hit with a melee attack it can use its reaction to force the target to make a DC16 dexterity saving throw. If the target fails the Adacthys throws it into the nearest hard surface and the target takes 6 (2d6) bludgeoning damage and is knocked prone.