Baby Tarrasque

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

Reflective Carapace. Any time the 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 1 to 5, the tarrasque is unaffected. On a 6, the 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 tarrasque deals double damage to objects and structures.

Multiattack. It then makes three attacks: one with its bite, and two with its claws. It can use its Swallow instead of its bite.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (1D10+3) piercing damage. If the target is a creature, it is grappled (escape DC 14). Until this grapple ends, the target is restrained and the tarrasque can’t bite another target.

Claw. Melee Weapon Attack: +5 to hit, reach 10ft., one target. Hit: 10 (1D10+5) slashing damage.

Swallow. The tarrasque makes one bite attack against a Small or Tiny 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 restrained, it has total cover against attacks and other effects outside the tarrasque, and it takes 25 (3D10+5); acid damage at the start of each of the tarrasque’s turns.

If the tarrasque takes 20 damage or more on a single turn from a creature inside it, the tarrasque must succeed on a DC 16 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone] in a space within 10 feet of the tarrasque.