One of the inspirations for monsters from the Book of Beasts: Legendary Foes is the idea of the ancient monster that sleeps and awakes once every [insert any large unit of time here] to devour the entire countryside. The millennial worm is one such monster. Once it eats its fill, it goes into a cocoon and transforms into a millennial tigermoth. This even deadlier monster also appears in the Book of Beasts: Legendary Foes, just in case the players fail to destroy the worm or locate its hidden lair before the monster reawakens.
With a white body larger than a house, this worm devours anything in its path.
Millennial Worm CR 15
N Gargantuan vermin
Init -1; Senses low-light vision, tremorsense 120 ft.; Perception +7
AC 30, touch 5, flat-footed 30 (-1 Dex, +25 natural, –4 size)
hp 231 (22d8+132)
Fort +19, Ref +6, Will +14
Defensive Abilities pliable body; DR 20/piercing; Immune mind-affecting effects
Speed 40 ft., burrow 40 ft.
Melee bite +28 (4d6+24 plus 4d6 acid plus grab)
Ranged acid spit +11 touch (10d6 acid)
Space 20 ft.; Reach 15 ft.
Special Attacks swallow whole (10d6 acid damage, AC 22, 29 hp)
Str 43, Dex 8, Con 22, Int —, Wis 25, Cha 2
Base Atk +16; CMB +36 (+40 grapple); CMD 45 (cannot be tripped)
Environment any forest, mountains, or underground
Organization solitary, pair, groveling (3-8)
Acid Spit (Ex) As a ranged touch attack with a range of 60 feet, a millennial worm can shoot its stomach acid at a target, priming it for digestion. Upon a successful ranged touch attack, the acid spit deals 10d6 points of acid damage.
Grab (Ex) A millennial worm can grab a creature of Medium size or smaller without gaining the grappled condition itself.
Pliable Body (Ex) A millennial worm’s body is soft and takes half damage from bludgeoning weapons after accounting for its damage reduction.
The deadly millennial tigermoth and worm were last seen a thousand years ago. Scholars recorded the widespread devastation these creatures brought upon the land with unmistakable fear in their words. Mere months after death came from below as the millennial worms sprang up and devoured everything they could find, terror came from the skies as eclipses of the millennial tigermoths blotted out the sun and decimated cities. The bravest warriors of the land hunted them down in their caves, killing these creatures and destroying their eggs. While most scholars believe their kind are long since eradicated, a few believe that these creatures still exist—and that their eggs should be hatching soon.