Anti Tarrasque Machine

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

Blade Resistance. The ATM has advantage on saving throws against slashing and piercing damage.

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

Siege Monster. This creature deals double damage to structures and building.

Magnetic Sword. The Anti Tarrasque Machine can use a bonus action to magnetically attract it's sword to its hands.

Multiattack. The ATM's can use its Frightful Presence. It then makes four attacks: one with its slam, two with its claws, one slam, and one with its tail. 

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

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

Frightful Presence. Each creature of the ATM's choice within 120 feet of it and aware of it must succeed on a DC 17 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, with disadvantage if the ATM's is within line of sight, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the ATM's Frightful Presence for the next 24 hours.

Slam. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 20 (8d8 + 7) bludgeoning damage.

 Fist. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (6d6 + 4) bludgeoning damage.

Clay Golem. ATM taps it's chest, which opens and out comes a Clay Golem.

Earthquake (Recharge 5-6). The Construct smashes the ground causing tremors in a 20 ft. radius. Each creature that isn't the ATM must make a DC 20 Dexterity saving throw. On a failed save the targets take 10d6 bludgeoning damage and is knocked prone. On a successful save the targets take half damage and is not knocked prone.Objects and Structures automatically fail the saving throw and take full damage. 

Tarrasque Slayer. Melee Weapon Attack: +6 to hit, reach 45 ft., one target. Hit: 54 (4d12 + 8) slashing damage, or 75 (6d12 + 8) slashing damage if used with two hands

The ATM can take 1 legendary action, choosing from the option below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The ATM regains spent legendary actions at the start of its turn.

 Detect. The ATM makes a Wisdom Perception check.