Tunneler. The worm can burrow through solid rock at half its burrow speed and leaves a 5-foot-diameter tunnel in its wake.

Multiattack. The worm makes two attacks: one with its bite and one with its stinger, these attacks cannot target the same creature.

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 14 (2d8 + 5) piercing damage. If the target is a Medium or smaller creature, it must succeed on a DC 16 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 9 (3d6) acid damage at the start of each of the worm's turns.

If the worm takes 25 damage or more on a single turn from a creature inside it, the worm must succeed on a DC 18 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 10 feet of movement, exiting prone.

Tail Stinger. Melee Weapon Attack: +7 to hit, reach 10 ft., one creature. Hit: 14 (2d8 + 5) piercing damage, and the target must make a DC 17 Strength saving throw, taking  11 (2d10) cold damage on a failed save, or half as much damage on a successful one. On a failed save the creature is pushed backwards 10ft.