Clockwork T-REX

Fire Absorption. Whenever the Clockwork T-Rex is subjected to fire damage, it takes no damage and instead regains a number of hit points equal to the fire damage dealt.

Immutable Form. The Clockwork T-Rex is immune to any spell or effect that would alter its form.

Magic Resistance. The Clockwork T-Rex has advantage on saving throws against spells and other magical effects.

Magic Weapons. The Clockwork T-Rex 's weapon attacks are magical.

Multiattack. The Clockwork T-REX makes two attacks: one with its bite and one with its tail. It can't make both attacks against the same target.

Bite Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 30 (4d12 + 7) Piercing damage.  If the target is a Large or smaller creature, it must succeed on a DC 20 Dexterity saving throw or be swallowed by the Clockwork T-Rex. A swallowed creature is blinded and restrained, it has total cover against attacks and other effects outside the Clockwork T-Rex, and it takes 21 (6d6) Fire damage at the start of each of the worm's turns.

If the Clockwork T-Rex takes 30 damage or more on a single turn from a creature inside it, the Clockwork T-Rex must succeed on a DC 21 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 Clockwork T-Rex. If the Clockwork T-Rex is destroyed, a swallowed creature is no longer restrained by it and can escape from the corpse by using 20 feet of movement, exiting prone.

Tail Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 23 (3d10 + 7)  damage.

Fiery Breath (Recharge 6). The Clockwork T-Rex exhales Fire in a 15-foot cone. Each creature in that area must make a DC 19 Constitution saving throw, taking 70 (15d8) Fire damage on a failed save, or half as much damage on a successful one.