Tarrasque

If the tarrasque fails a save, it can choose to succeed instead.

The tarrasque has advantage on saves against spells and other magical effects.

The tarrasque is resistant to exhaustion.

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.

The tarrasque deals triple damage to objects and structures.

Ranged Weapon Attack: +12 to hit, range 100/400 ft., one target. Hit: 36 (6d10+3) acid damage.

Melee Weapon Attack: +19 to hit, reach 10 ft., one target. Hit: 36 (4d12+10) piercing damage. If the target is a creature, it must succeed on a DC 27 DEX save or be swallowed by the tarrasque. A swallowed creature is blinded and restrained, it has total cover against attacks and other effect outside of the tarrasque, and it takes 42 (12d6) 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 CON save 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 using 20 feet of movement, exiting prone.

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

Each creature of the tarrasque's choice within 120 feet of it and aware of it must succeed on a DC 27 WIS save or be frightened for 1 minute. A creature can repeat the save at the end of each of its turns, ending the effect on itself on a success. If a creature's save is successful or the effect ends for it, the creature is immune to the tarrasque's Frightful Presence for the next 24 hours.

The tarrasque uses its Frightful Presence. It then makes one Bite attack, four Claw attacks, and one Spiked Tail attack, or it makes five Acid Spit attacks.

Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 20 (3d6+10) bludgeoning damage and 13 (3d8) piercing damage. If the target is a creature, it must succeed on a DC 27 STR save or be knocked prone.

The tarrasque whips its spiked tail in a wide arc, flailing it in a 30-foot cone. Each creature in that area must make a DC 27 DEX save. On a failure, a creature takes 45 (10d8) piercing damage and is knocked prone. On a success, a creature takes half the damage and isn't knocked prone.

The tarrasque automatically detects every creature and trap within 60 feet of it, pinpointing the current location of each.

The tarrasque moves up to its speed without provoking opportunity attacks.

The tarrasque makes one Tail attack.

The tarrasque whips its spiked tail in a wide arc, flailing it in a 30-foot cone. Each creature in that area must make a DC 27 DEX save. On a failure, a creature takes 45 (10d8) piercing damage and is knocked prone. On a success, a creature takes half the damage and isn't knocked prone.