Multiattack. The crab makes two Claw attacks and one Stinger attack.

Claw. Melee Weapon Attack: +10 to hit, reach 15 ft., one target. Hit: 19 (3d8 + 6) bludgeoning damage. If the target is a Huge or smaller creature, it has the grappled condition (escape DC 16). The crab has four claws, each of which can grapple one target.

Stinger. Melee Weapon Attack: +10 to hit, reach 10 ft., one creature. Hit: 22 (3d10 + 6) piercing damage, and the target must succeed on a DC 17 Constitution saving throw or have the poisoned and paralyzed conditions for 1 minute. The affected creature can repeat the saving throw at the end of each of its turns, ending both the poisoned and paralyzed conditions on itself on a success.

Water Jet (Recharge 5–6). The crab exhales water in a 150-foot line that is 10 feet wide. Each creature in that area must make a DC 17 Dexterity saving throw. On a failed save, a creature takes 27 (6d8) bludgeoning damage, is pushed up to 30 feet from the crab, and has the prone condition. On a successful save, a creature takes half as much damage only.