Chaos-Born Tarrasque

Legendary Resistance (3/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.

Siege Monster. The tarrasque deals double damage to objects and structures.

Chaos Surge. The tarrasque creates a huge surge of wild magic, caused by taking more than 40 damage in 1 turn, Getting below 700, 500, 300, 100 and 0 hp , or when a creature level or challenge rating 10 or higher dies within 60 ft of the tarrasque. Consult the table for what effect occurs.

Roll 1d8

1. The tarrasque and every creature within 80ft of it are teleported to a random location on the material plane, or, if they are already there, 2d20 miles in a random direction. 
2. Every creature within 120 ft. takes 2d12 lighting damage, 3d10 fire damage and 4d8 force damage as they are hurled 1d100 ft away from the tarrasque.
3. A glowing red eye opens on a random location on the Tarrasque's body. One random creature within 120 ft of the tarrasque is hit by a laser from that eye, taking 4d20 fire damage which ignores resistance and treats immunity as resistance.
4. The tarrasque roars, and 1d12 wyverns fly out of its mouth.
5. For the next 1d20 hours the tarrasque gains a flying speed of 80 ft.
6. Water flows out of the pores in the tarrasques skin. all creature in a 90 ft radius of the tarrasque must make a DC 20 strength saving throw or be moved outside of that radius (they move 20 ft or outside of the radius on a success, whichever is closer).
7.  Smoke bellows out of the tarrasques mouth which lasts for 1d4 rounds. All creatures within a 50 ft high 90 ft diameter sphere are blinded for 1d8 rounds.
8. The tarrasque begins to leak bubbles. Any creature that touches the tarrasque takes 1d12 poison damage. That includes melee attacks the tarrasque makes against creatures.

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.

Bite. Melee Weapon Attack: +19 to hit, reach 10 ft., one target. Hit: 42 (6d12 + 11) piercing damage. If the target is a creature, it is grappled (escape DC 21). Until this grapple ends, the target is restrained, and the tarrasque can’t bite another target.

Claw. Melee Weapon Attack: +19 to hit, reach 15ft., one target. Hit: 36 (5d8 + 15) slashing damage.

Horns. Melee Weapon Attack: +19 to hit, reach 10ft., one target. Hit: 39 (5d12 + 7) piercing damage.

Tail. Melee Weapon Attack: +19 to hit, reach 20ft., one target. Hit: 24 (4d6 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 21 Strength saving throw or be knocked 20 ft away from the tarrasque and be prone.

Frightful Presence. Each creature of the tarrasque’s choice within 120 feet of it and aware of it must succeed on a DC 17 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 56 (16d6) 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.

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.