TEXT: The Mega Tarrasque
  T
  he epic mega tarrasque is possibly the most
  dreaded monster in the cosmos. It is widely
  believed that only one of these creatures
  exists, though no one can predict where and
  when it will strike. A scaly biped, the tarrasque
  is 500-feet tall and nearly 1,000 feet long,
  weighing thousands of tons. It carries itself
  like a bird of prey, leaning forward and using its powerful
  lashing tail for balance (and mass destruction). Its cavernous
  maw yawns wide enough to swallow even gargantuan
  creatures, and so great is its hunger that it can devour the
  populations of entire worlds.
  Epic Destruction. The destructive potential of the mega
  tarrasque is so vast that it’s been known to destroy entire
  worlds while rampaging.
  Only planars speak of how the epic, mega tarrasque
  lumbers in its secret lair beyond the realms, remaining in a
  dormant state for centuries and millennia. When it awakens
  in answer to some inscrutable cosmic call, it rises from the
  depths to obliterate everything in its path.
  Epic Creature. The mega tarrasque is an epic creature. It
  has three main parts: basic statistics which apply to all
  elements of the creature, body parts, and action options. If
  the tarrasque's brain is destroyed, it is destroyed and cannot
  take actions.
  Into the Tarrasque. This stat block is part of the upcoming
  "Into the Tarrasque" storyline presented by 26+ creatores,
  due out in the January issue of BroadSword Monthly.
  1
  The Mega Tarrasque
  Epic monstrosity (500-feet tall, 1,000-feet long),
  unaligned
  Travel Pace 40 miles per hour (400 miles per day)
  STR
  DEX
  CON
  INT
  WIS
  CHA
  30 (+10) 11 (+0) 30 (+10) 3 (-4) 11 (+0) 11 (+0)
  Saving Throws Int +5, Wis +9, Cha +9
  Skills Perception +18
  Damage Immunities fire, poison; bludgeoning, piercing,
  and slashing from nonmagical attacks
  Condition Immunities charmed, frightened, paralyzed,
  poisoned
  Senses blindsight 1,000 ft., passive Perception 28
  Languages -
  Challenge 80 (1,655,000 XP)
  Epic Creature. The tarrasque makes all ability checks,
  attack rolls, and saving throws with advantage. If the
  tarrasque rolls a 1 while making an attack, it does not
  count as a critical failure. In addition, all of the
  tarrasque’s senses extend up to five miles.
  Magic Resistance. The tarrasque and all of its parts have
  advantage on saving throws agaifnst spells and other
  magical effects.
  Siege Monster. The tarrasque and all of its parts deal
  double damage to objects and structures.
  Actions and Legendary Actions
  On its turn, the tarrasque can take 6 actions, choosing
  from the options below. 
      In addition, the tarrasque can take 3 legendary
  actions, choosing from the same options. Only one
  legendary action 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.
  Bite (Costs 2 Actions, 2/Turn). The tarrasque can use its
  brain to bite with its head.
  Claws. The tarrasque can use its brain to attack with
  one of its claws.
  Horns (1/Turn). The tarrasque can use its brain to attack
  with its horns.
  Frightful Presence (1/Turn). The tarrasque can use its
  brain to use its Frightful Presence.
  Move. The tarrasque can use its brain to move with its
  legs.
  Tail (Costs 2 Actions). The tarrasque can use its brain to
  attack with its tail.
  Shell
  Armor Class 30 (natural armor)
  Hit Points 2,000 (damage threshold 100)
  Damage Immunities psychic
  Legendary Resistance (3/Day): If the tarrasque’s shell
  fails a saving throw, the tarrasque can choose to
  succeed instead.
  Massive Target: The tarrasque’s carapace takes up the
  majority of its body. As such, all of its body parts have
  1/2 cover against attacks made it against them
  (included in the description). In addition, any magic
  missile spell, a line spell, or ranged attack roll that
  misses a non-shell part of the tarrasque, has a chance
  of reflecting back on the caster (see below).
  Reflective Carapace: Any time the tarrasque’s shell 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 or 5,
  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.
  Control: Brain
  Armor Class 19 (natural armor, shell cover)
  Hit Points 250
  Damage Vulnerabilities psychic
  The Mega Tarrasque | DMDave
  
  2
  The brain can be attacked only if the head has taken
  400 or more damage. If the brain is damage or
  destroyed, the tarrasque and all of its parts can’t take
  actions or legendary actions.
  Frightful Presence: Each creature of the tarrasque’s
  choice within 1,000 feet of it and aware of it must
  succeed on a DC 22 Wisdom saving throw or become
  frightened for 1 minute. A creature can repeat the
  saving throw at the end of each of its turns, 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.
  Legendary Resistance (3/Day): If the tarrasque’s brain
  fails a saving throw, the tarrasque can choose to
  succeed instead.
  Movement: Legs
  Armor Class 27 (natural armor, shell cover)
  Hit Points 800 (damage threshold 40); -5 ft. speed per
  200 damage taken
  Damage Immunities psychic
  Speed (land) 40 ft.
  Destructive Path: As the tarrasque moves, it can enter
  Gargantuan or smaller creatures’ spaces. Whenever the
  tarrasque enters a creature’s space, it must make a DC
  27 Dexterity or Strength saving throw (target’s choice).
      On a failed save, the tarrasque enters the creature’s
  space, and the creature takes 37 (6d8 + 10) piercing
  damage plus 37 (6d8 + 10) bludgeoning damage and
  falls prone in the tarrasque’s space. 
      On a successful save, the creature only takes half as
  much damage, isn’t knocked prone, and is pushed 5
  feet out of the tarrasque’s space into an unoccupied
  space of the creature’s choice. If no unoccupied space
  is within range, the creature instead falls prone in the
  tarrasque’s space.
  Legendary Resistance (3/Day): If the tarrasque’s legs fails
  a saving throw, the tarrasque can choose to succeed
  instead.
  Weapon: Head
  Armor Class 27 (natural armor, shell cover)
  Hit Points 800 (damage threshold 40)
  Bite: Melee Weapon Attack: The tarrasque targets a
  point that it can see within 100 feet of it, biting
  everything in a 20-foot cube centered on that point.
  Each creature in the area must make a DC 27 Dexterity
  saving throw. On a failed saving throw, a target takes
  88 (12d12 + 10) piercing damage and enters the
  Tarrasque’s Mouth (area 1).
     On a successful save, the target can choose to be
  pushed 5 feet back from the bite area and takes half
  the piercing damage. A creature that can’t be pushed
  or chooses not to be pushed suffers the consequences
  of a failed saving throw.
  Horns: Melee Weapon Attack: +19 to hit, reach 100 ft.,
  one target. Hit: 76 (12d10 + 10) piercing damage.
  Legendary Resistance (3/Day): If the tarrasque’s head
  fails a saving throw, the tarrasque can choose to
  succeed instead.
  Weapon: Claw (2)
  Armor Class 27 (natural armor, shell cover)
  Hit Points 600 (damage threshold 30)
  Damage Immunities psychic
  Claw: Melee Weapon Attack: The tarrasque targets a
  point that it can see within 150 feet of it, clawing
  everything in a 20-foot by 20-foot square centered on
  that point. Each creature in the area must make a DC
  27 Dexterity saving throw, taking 64 (12d8 + 10)
  slashing damage on a failed saving throw, or half as
  much damage on a successful one.
  Legendary Resistance (3/Day): If the tarrasque’s claws
  fails a saving throw, the tarrasque can choose to
  succeed instead.
  Weapon: Tail
  Armor Class 25 (natural armor)
  Hit Points 1,000 (damage threshold 100)
  Damage Immunities psychic
  Tail Thrash: Melee Weapon Attack: The tarrasque swings
  its tail. Each creature in a 200-foot cube originating
  from the tarrasque must make a DC 27 Dexterity
  saving throw. On a failed saving throw, a creature takes
  52 (12d6 + 10) bludgeoning damage and is flung up
  800 feet away from the tarrasque in a random direction
  and knocked prone. If a thrown target strikes and an
  object such as a wall or floor, the targets takes 3 (1d6)
  bludgeoning damage for every 10 feet it was thrown. if
  the target is thrown at another creature, that creature
  must succeed on a DC 13 Dexterity saving throw or
  take the same damage and be knocked prone. 
     If the saving throw is successful, the target takes half
  the bludgeoning damage and isn’t flung away or
  knocked prone.
  Legendary Resistance (3/Day): If the tarrasque’s tail fails
  a saving throw, the tarrasque can choose to succeed
  instead.
  
SOURCE: textdata/thevault/Dungeons & Dragons [multi]/5th Edition (5e)/3rd Party/DmDave/DMDave - Mega Tarrasque.pdf