Cumeria, the Arch Hollow

Saving Throws. Int +18, Wis +22, Cha +22

Titanic. This creature is larger than Gargantuan and takes up a 90 ft. by 90 ft. area.

Winged. And just as you though things couldn't get any worse.

Innate Spellcasting. The tarrasque's innate spellcasting ability is Charisma. It can cast [Tooltip Not Found] and plane shift (targeting only itself) at will.

Legendary Resistance (5/Day). If the tarrasque fails a saving throw, it can choose to succeed instead.

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.

Prescient. The tarrasque cannot be surprised and always goes first in initiative order.

Augmented Critical. The tarrasque's attacks score a critical hit on a die roll of 18–20, and on a critical hit it rolls damage dice three times, instead of twice.

Earthbind Aura. Creatures with a fly speed within 1 mile of the tarrasque have their fly speed reduced to 0. If a creature is in midair when it becomes affected by Earthbind Aura, it falls at a rate of 60 feet per round until it reaches the ground.

Elder of Annihilation. The tarrasque ignores all other creatures' damage resistances and immunities.

Eternal Slumber. When the tarrasque is reduced to 0 hit points, it sinks back into the earth's core and slumbers once again.

Surefooted. The tarrasque has advantage on saving throws made against effects that would knock it prone.

Trample. When the tarrasque enters any enemy's space for the first time on a turn, the enemy must succeed on a DC 19 Dexterity saving throw or take 31 (6d6+10) bludgeoning damage and be knocked prone.

 Multiattack. The tarrasque can use its Frightful Presence. It then makes five attacks: one with its bite, two with its claws, one with its horns, and one with its tail. It can use its Swallow instead of its bite. Alternatively, it makes three rock attacks.

Bite. Melee Weapon Attack: +24 to hit, reach 20 ft., one target. Hit: 49 (6d12 + 10) piercing damage. If the target is a creature, it is grappled (escape DC 20). Until this grapple ends, the target is restrained, and the tarrasque can't bite another target.

Claw. Melee Weapon Attack: +24 to hit, reach 25 ft., one target. Hit: 37 (6d8 + 10) slashing damage.

Horns. Melee Weapon Attack: +24 to hit, reach 20 ft., one target. Hit: 43 (6d10 + 10) piercing damage.

Tail. Melee Weapon Attack: +24 to hit, reach 30 ft., one target. Hit: 31 (6d6 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 32 Strength saving throw or be knocked prone.

Rock. Ranged Weapon Attack: +24 to hit, range 360/1440 ft., one target. Hit: 49 (6d12 + 10) bludgeoning damage.

Frightful Presence. Each creature of the tarrasque's choice within 240 feet of it and aware of it must succeed on a DC 30 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 tarrasque 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 tarrasque's Frightful Presence for the next 24 hours.

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 84 (24d6) acid damage at the start of each of the tarrasque's turns.
If the tarrasque takes 60 damage or more on a single turn from a creature inside it, the tarrasque must succeed on a DC 20 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.

Annihilation Breath (Recharge 5-6). The tarrasque exhales pure energy in a 240-foot cone. Each creature in that area must make a DC 32 Constitution saving throw, taking 119 (34d6) force damage on a failed save, or half as much damage on a successful one. If this damage reduces the target to 0 hit points, it is disintegrated. A disintegrated creature is reduced to a pile of fine gray dust. The creature can be restored to life only by means of a true resurrection or a wish spell. The tarrasque's annihilation breath automatically disintegrates nonmagical objects or creations of magical force.

The tarrasque can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The tarrasque regains spent legendary actions at the start of its turn.

Attack. The tarrasque makes one claw attack or tail attack.

Move. The tarrasque moves up to half its speed.

Chomp (Costs 2 Actions). The tarrasque makes one bite attack or uses its Swallow.

An Inevitable End. Cumeria is truly immortal, a force of nature that was here long before any of the gods. And she will remain here until the end of time. If she is reduced to 0 hit points, she returns to sleep for the next 10,000 years. Unable to be affected by anything, unable to be hurt by any means.