Brown Worm

Sand-Burrower. The brown worm can burrow through sand and earth at its burrow speed, but not solid rock.

Multiattack. The brown worm can make a bite attack and up to two attacks with its tendril mouths.

Bite. Melee Weapon Attack: +11 to hit, reach 10ft., 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 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: 13 (1d8 + 9) bludgeoning damage, and the target must make a DC 11 Strength saving throw or be grappled by the worm. If the target is grappled by the worm at the start of the worm's turn, they must succeed on a DC 19 Dexterity saving throw or be swallowed by the worm, as the worm's bite attack.