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.

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

Bite. Melee Weapon Attack: +5 to hit, reach 5ft., one target.  (2d12 + 4) piercing damage. If the target is a creature, it is grappled (escape DC 15). Until this grapple ends, the target is restrained, and the tarrasque can't bite another target.

Claw. Melee Weapon Attack: +5to hit, reach 5ft., one target.  (2d8 + 4) slashing damage.

Horns. Melee Weapon Attack: +5 to hit, reach 5ft., one target.  (1d10 + 4) piercing damage.

Swallow. The tarrasque 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 tarrasque, and it takes 24(6d6) 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 15 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. If the tarrasque dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.