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

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

Reflective Carapace. Any time the MechaTarrasque 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, the MechaTarrasque is unaffected. On a 6, the MechaTarrasque is unaffected, and the effect is reflected back at the caster as though it originated from the MechaTarrasque, turning the caster into the target.

Reanimation. The MechaTarrasque regains 40 hit points at the start of its turn. When it is killed, it must take 50 or more points of damage before the start of its next turn, otherwise it returns to life with 100 hit points.

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

Multiattack. The MechaTarrasque can use its Frightful Presence. It then makes five attacks: one with its bite, two with its claws, one with its horns, and one with its tail. It can use its Swallow instead of its bite.

Bite. Melee Weapon Attack: +19 to hit, reach 10 ft., one target. Hit: 36 (4d12 + 10) piercing damage. If the target is a creature, it is grappled (escape DC 20). Until this grapple ends, the target is restrained, and the MechaTarrasque can't bite another target.

Claw. Melee Weapon Attack: +19 to hit, reach 15ft., one target. Hit: 28 (4d8 + 10) slashing damage.

Horns. Melee Weapon Attack: +19 to hit, reach 10ft., one target. Hit: 32 (4d10 + 10) piercing damage.

Tail. Melee Weapon Attack: +19 to hit, reach 20ft., one target. Hit: 24 (4d6 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 20 Strength saving throw or be knocked prone.

Eye laser (Recharge 5-6). Each creature in a 120ft long, 10ft wide line originating from the MechaTarrasque must make a dexterity saving throw (DC 18), taking 65 (10d10 + 10) fire damage on a failed save, or half as much on a successful one.

Swallow. The MechaTarrasque makes one bite attack against a Large or smaller creature it is grappling. If the attack hits, the target takes the bite's damage, the target is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the MechaTarrasque, and it takes 70 (20d6) acid damage at the start of each of the MechaTarrasque's turns.

If the MechaTarrasque takes 60 damage or more on a single turn from a creature inside it, the MechaTarrasque must succeed on a DC 18 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, as well as spawning and regurgitating 2 Skeletons, all of which fall prone in a space within 10 feet of the MechaTarrasque. If the MechaTarrasque dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.

The MechaTarrasque 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 MechaTarrasque regains spent legendary actions at the start of its turn.

Attack. The MechaTarrasque makes one claw attack or tail attack.

Move. The MechaTarrasque moves up to half its speed.

Chomp (Costs 2 Actions). The MechaTarrasque makes one bite attack or uses its Swallow.

Blast (Costs 3 Actions). The MechaTarrasque uses its Eye Laser ability.