Brown Worm

Tunneler. The worm can burrow through sand and earth at half its burrow speed and leaves a 10-foot-diameter tunnel in its wake.

Desert Hunter. The Brown worm cannot tunnel through solid rock.

Multiattack. The worm makes two attacks: one with its bite and one with its stinger.

Bite. Melee Weapon Attack: +14 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.

Tendril mouths. Melee weapon attack: +14 to hit, reach 15ft., one target. Hit: 22 (4d6+9) piercing damage.

The Brwon Worm can make Perception checks to detect anyone treading on sand or earth within 200 feet with no penalty.