Legendary Resistance (6/Day). If the tarrasque fails a saving throw, it can choose to succeed instead.

Magic Resistance. The tarrasque has Advantage on saving throws against spells and other magical effects.

Reflective Carapace. If the tarrasque is targeted by a Magic Missile spell or a spell that requires a ranged attack roll, roll 1d6. On a 1-5, the tarrasque is unaffected. On a 6, the tarrasque is unaffected and reflects the spell, turning the caster into the target.

Siege Monster. The tarrasque deals double damage to objects and structures.

Bite. Melee Attack Roll: +19, reach 15 ft. 36 (4d12 + 10) Piercing damage, and the target has the Grappled condition (escape DC 20). Until the grapple ends, the target has the Restrained condition and can't teleport.

Claw. Melee Attack Roll: +19, reach 15 ft. 28 (4d8 + 10) Slashing damage.

Multiattack. The tarrasque makes one Bite attack and three other attacks, using Claw or Tail in any combination.

Tail. Melee Attack Roll: +19, reach 30 ft. 23 (3d8 + 10) Bludgeoning damage. If the target is a Huge or smaller creature, it has the Prone condition.

Thunderous Bellow. Constitution Saving Throw: DC 27, each creature and each object that isn't being worn or carried in a 150-foot Cone. Failure: 78 (12d12) Thunder damage, and the target has the Deafened and Frightened conditions until the end of its next turn. Success: Half damage only.

Onslaught. The tarrasque moves up to half its Speed, and it makes one Claw or Tail attack.

World-Shaking Movement. The tarrasque moves up to its Speed. At the end of this movement, the tarrasque creates an instantaneous shock wave in a 60-foot Emanation originating from itself. Creatures in that area lose Concentration and, if Medium or smaller, have the Prone condition. The tarrasque can't take this action again until the start of its next turn.