Baby Tarrasque

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

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

Siege Monster. The baby tarrasque deals double damage to objects and structures that are smaller than it.

Multiattack. It then makes four attacks: one with its bite, one with its claws, one with its horns and one with its tail. It can use its Thrash instead of its bite.

Bite. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 20 (2d12 + 7) piercing damage. If the target is a creature of size Medium or smaller, it is grappled (escape DC 17). Until this grapple ends, the target is restrained, and the baby tarrasque can't bite another target.

Claw. Melee Weapon Attack: +12 to hit, reach 10ft., one target. Hit: 28 (3d8 + 7) slashing damage.

Horns. Melee Weapon Attack: +12 to hit, reach 5ft., one target. Hit: 18 (2d10 + 7) piercing damage.

Tail. Melee Weapon Attack: +11 to hit, reach 10ft., one target. Hit: 14 (3d6 + 7) bludgeoning damage. If the target is a creature, it must succeed on a DC 17 Strength saving throw or be knocked prone

Thrash. The baby tarrasque makes one bite attack against a Medium of smaller creature it is grappling. If the attack hits, the target takes the bite's damage and the target, on its turn, can use either an action or a bonus action, not both. Regardless of the target's abilities or magic items, it can't make more than one melee or ranged attack during its turn.