Almighty Amethyst 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.

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.

Amethyst Armor. At the beginning of the monster's turn, it rolls a d20. If it rolls an 11 or above its armor class increases by 3 for the next turn. (This wears off at the end of the round). If it rolls a 10 or under, it deals 37 damage to itself. This damage cannot be avoided.

Bite. Melee Weapon Attack: +19 to hit, reach 10 ft., one target. Hit: 36 (4d12 + 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: +19 to hit, reach 15ft., one target. Hit: 28 (4d8 + 10) slashing damage.

Horns. Melee Weapon Attack: +19 to hit, reach 10ft., one target. Hit: 32 (4d10 + 10) 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 20 Strength saving throw or be knocked 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.

Gatling Geode. Ranged Weapon Attack, +9 to hit, range 10/50ft. line, hits as many targets in the "spash zone". Shoots multiple small amethyst crystals in a straight line. Players within the outer edge of the spash zone must roll a DC 10 dexterity saving throw. On a success, they take no damage, on a failure they make a Constitution check, the lower the roll is the more 1d10's they have to roll. Players within the spash zone must roll a DC 17 dexterity saving throw, on a success, they take the damage of failing the saving throw of the outer edge, on a fail they make the same constitution check, but the damage dice amount is 2d10. If you roll a critical hit, it does not affect the damge.

Destructive Desire. It recalls all the crystals shot in a straight line. If any creature survives they will have to roll another DC 13 dexterity saving throw, and they take no damage on a successful save, on a fail they take 2d20+17 piercing damage. After the crystals are recalled, it roars, stunning ever creature on the field, and fires amethyst at them, dealing 1d20 piercing damage to each player, however, if there are 5 or less players, this attack will deal 3d20 piercing damage.

Death Wish (1/Day). This move can be used only if the party already has 5 faints/deaths. It is locked behind death. Giant amethyst spikes fly out of the ground. She causes giant amethyst spikes to come out of the ground, in a circle around her. She then recalls all her amethyst to form a sphere around here. The player must roll a DC 13 Dexterity Saving Throw. On a failure, they take (5d6) piercing damage, and on a sucess you dodge the spikes, and take no damage. IF you are hit by the spikes you are pushed close to the beast, and you are knocked prone for 5 turns. If you are knocked prone, you take (1d4) . After this move, if it has the option, it will use a powered up version of amethyst beam.Which removes the option for saving throws, and the beam deals double damage.

Untouchable Armor. Upon reaching 15% health, the creature a 2d8 damage buff, and it will be unable to take any form of damage for 2 rounds.

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.

The tarrasque has 10 mythical actions, which regenerate every round, for only 2 rounds.

Amethyst Beam (Costs 10 actions). The creature has all the amethyst surround its upper body (or so) area, and it roars. All the amethyst gets fired in a 300ft line. Any players in this line must roll a DC 16 Dexterity saving throw. They take 7d20+15 piercing damage. If the amethyst beam is used, it uses destructive desire as a bonus action.