Tunneler. The worm can burrow through solid rock at a quarter of its burrow speed and leaves a 10-foot-diameter tunnel in its wake.

Multiattack. The worm makes two bite attacks.

Bite. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 19 (2d8 + 10) piercing damage. If the target is a Large or smaller creature, it must succeed on a DC 14 Dexterity saving throw or be swallowed by the worm. A swallowed creature is blinded, prone, and restrained. It has total cover against attacks and other effects outside the worm, and it takes 21 (4d6) 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 24 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 15 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.

Constrict. Melee Weapon Attack: +9 to hit, reach 5 ft., any Large or smaller creatures within 5 ft. of the Young Sonari Worm. Hit: 12 (2d6 + 5) bludgeoning damage plus 17 (2d8 + 8) slashing damage. The target is grappled (escape DC 14) if the Young Sonari Worm isn't already constricting a creature, and the target is blinded until this grapple ends. The Young Sonari Worm may not burrow while grappling a creature.

Sand Blast. If the Young Sonari Worm uses its full burrowing speed, it sprays a line of sand that is 25 feet long and 10 feet wide. Each creature in that line must make a DC 15 Dexterity saving throw, taking 11 (2d10) piercing damage on a failed save, or half as much damage on a successful one. On a failed save, creatures must make a DC 12 Constitution saving throw, or gain disadvantage on ability checks and attack rolls until the end of their next turn.