Gargantuan monstrosity, unaligned
- Armor Class 20 (natural armor)
- Hit Points 247 (15d10+90)
- Speed 50 ft., burrow 50ft.
- Saving Throws Con +10, Wis +3
- Senses blindsight 30 ft., tremorsense 120 ft., passive Perception 9
- Challenge 12 (8,400 XP)
- Tunneler. The worm can burrow through solid rock at half its burrow speed and leaves a 20-foot-diameter tunnel in its wake.
- Tremors. As the worm approaches, the earth begins to shake in a 60ft Radius around it's breach point. At the start of their turn all creatures must make a DC 19 Dexterity Saving Throw or move at half speed until their next turn.
- Multiattack. The worm makes two attacks: one with its bite and one with its tail.
- Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 22 (3d8 + 9) piercing damage. If the target is a Large or smaller creature, it must succeed on a DC 19 Dexterity saving throw or be swallowed by the worm. A swallowed creature is blinded and restrained, it has total cover against attacks and other effects outside the worm, and it takes 21 (6d6) acid damage at the start of each of the worm's turns. If the worm takes 30 damage or more on a single turn from a creature inside it, the worm must succeed on a DC 21 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 worm. If the worm dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 20 feet of movement, exiting prone.
- Tail Slam. Melee Weapon Attack: +9 to hit, reach 15ft cone., any creature within. Hit: 19 (3d6 + 9) bludgeoning damage, and the target must make a DC 19 Dexterity saving throw, taking 21 (6d6) bludgeoning damage on a failed save and become prone, or half as much damage on a successful one and avoid being knocked prone.