Battlefield Carrion Crab

Shell Break. When the crab takes 25 or more damage from a single attack, its shell cracks. Its AC becomes 15, it regains 10 hit points, and it enters its Enraged state.

Enraged (Phase 2). While enraged, the crab’s speed increases to 40 ft., it makes one additional claw attack when it uses Multiattack, and its Acid Spew recharge improves to 4–6.

Legendary Resistance (1/Day). If the crab fails a saving throw, it can choose to succeed instead.

Amphibious: This beast can breathe in air and water.

Corpse Feeder. When the crab starts its turn in an area containing a Medium or larger corpse, it regains 5 hit points as it devours the dead flesh.

Multiattack The crab makes two Claw attacks. (Three when Enraged.)

Claw Melee Attack Roll: +7, reach 10 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage. If both claws hit the same target in a turn, that target is grappled (escape DC 15).

Crush One creature grappled by the crab must make a Constitution Saving Throw: DC 15. Failure: 13 (3d6 + 4) bludgeoning damage. Success: Half damage.

Acid Spew (Recharge 5–6). The crab spits digestive acid in a 15-foot cone. Each creature in that area must make a Constitution Saving Throw: DC 14. Failure: 9 (2d6 + 2) acid damage. Success: Half damage. (Recharge improves to 4–6 when Enraged.)

The crab can take 1 legendary action, 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 crab regains spent legendary actions at the start of its turn.

Move.
The crab moves up to half its speed without provoking opportunity attacks.

Claw Melee Attack Roll: +7, reach 10 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage. If both claws hit the same target in a turn, that target is grappled (escape DC 15).

Burrow Skitter (costs 1 action).
The crab burrows into the ground and reemerges within 20 feet.
Its next attack before the end of its next turn is made with advantage.