Crabzilla

Rival TItan. Crabzilla is the sworn enemy of the Kraken and the Tarrasque.

Summoned. Crabzilla sleeps in a special plane that only it can enter. It is summoned to the material plane when a statue of a crab 20 ft. tall or higher is struck with lightning (not from spells) three times within the same minute. If the Tarrasque awakens, the statue only needs to be struck once, and lightning from spells work.

Legendary Resistance (3/Day). If Crabzilla fails a saving throw, it can choose to succeed instead.

Magic Resistance. Crabzilla has advantage on saving throws against spells and other magical effects.

Reflective Carapace. Any time Crabzilla is targeted by a magic missile spell, a line spell, or a spell that requires a ranged attack roll, roll a d6. On a 1 to 5, Crabzilla is unaffected. On a 6, Crabzilla is unaffected, and the effect is reflected back at the caster as though it originated from Crabzilla, turning the caster into the target.

 Siege Monster. Crabzilla deals double damage to objects and structures.

Last Resort. If Crabzilla is defeated, it explodes in a gigantic flaming mushroom cloud. It instantly kills anything within 500 ft. with an armor class of 24 or lower, and creatures within that radius with an armor class of 25 or higher take 200 (10d20) fire damage and 200 (10d20) bludgeoning damage. anything outside the 500 ft. radius within a 1000 ft. radius take 60 (5d6) radiant damage from the initial explosion, rolling 1d10 for radiant damage at the end of every turn or minute after the explosion or until they succeed on a DC24 CON saving throw or take a long rest.

Multiattack. Crabzilla makes two step attacks.

Step. Melee weapon attack: range: 10 ft., one target. Target must make a DC15 DEX saving throw. Upon failure, They take 26 (5d6) Bludgeoning damage, 5 (1d6) piercing damage, and 10 (1d12) necrotic damage, and upon a successful save, the target takes half as much of the bludgeoning and piercing damage, and no necrotic damage. any plant life that Crabzilla steps on withers and dies.

Crabzilla can take 3 legendary actions per round, and used legendary actions are replenished on its turn.

Step. Crabzilla makes a step attack.

Wail. Crabzilla lets out a warbling screech. every creature within a 300 ft. radius must make a DC20 CON saving throw, and on failure, they must take 30 (5d6) thunder damage, or half as much on a successful save.

Lasers. Crabzilla must have used its wail attack as its previous action to use its lasers. When it does, a beam of turquoise energy shoots from its claws. All targets (25 targets max) must make a DC20 DEX saving throw, taking 100 (16d6+9) force damage on a failure or half as much on a success.