Amphibious. The crab can breathe air and water.
Shell Camouflage. While the crab remains motionless with its eyestalks and pincers tucked close to its body, it resembles a natural formation or a pile of detritus. A creature within 30 feet of it can discern its true nature with a successful DC 15 Intelligence (Nature) check.
Multiattack. The crab makes two attacks with its claws.
Claw. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit:20 (3d10 + 4) bludgeoning damage, and the target is grappled (escape DC 15). The crab has two claws, each of which can grapple only one target
Much bigger than a giant crab, a hulking crab has a body 15 to 20 feet in diameter. Its shell is often covered with coral, anemones, ship wreckage, or some other sort of detritus salvaged from the ocean floor.