Amphibious. The coral crawler can breathe air and water.

Shell Camouflage. While the coral crawler is withdrawn, it resembles a coral reef or a sunken ship. A creature within 30 feet of it can discern its true nature with a successful DC 15 Intelligence (Nature) check.

Siege Monster. The coral crawler deals double damage to objects and structures.

Multiattack. The coral crawler makes two claw attacks and one bite attack.

Bite. Melee Weapon Attack: +12 to hit, reach 5 ft., one grappled target. Hit: 25 (3d12 + 6) piercing damage. The target must succeed on a DC 18 Constitution saving throw or be poisoned for 1 minute. Until this poison ends, the target is blinded and deafened.

Claw. Melee Weapon Attack: +12 to hit, reach 15 ft., one target. Hit: 32 (4d12 + 6) bludgeoning damage. The target is grappled (escape DC 20) if it is a Huge or smaller creature and the coral crawler doesn't have two other creatures grappled.

Water Jet (Recharge 5–6). The coral crawler exhales power stream of water in a 60-foot line that is 5 feet wide. Each creature in that area must make a DC 18 Strength saving throw. On a failed save the creature takes 90 (20d8) bludgeoning damage and is knocked back 15 feet. On a success the creature takes half as much damage and is not knocked back.

The coral crawler can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The coral crawler regains spent legendary actions at the start of its turn.

Bite. The coral crawler makes one bite attack.

Smash. If the coral crawler has two creatures grappled it smashes them together, dealing 19 (2d12 + 6) bludgeoning damage.

Withdraw (Costs 3 Actions). The coral crawler withdraws into its shell. While withdrawn, it has resistance to all damage, and it is restrained. At the end of its next turn, it emerges free of all conditions and regains 52 (5d20) hit points.