Adult Lava Worm

Tunneler. The worm can burrow through solid rock at half its Burrow Speed and leaves a 10-foot-diameter tunnel in its wake. The walls of the tunnel radiate intense heat for 1 minute, causing 10 (2d6+2) Fire damage to any creature that starts its turn within the tunnel.

Fire Aura. The worm's body radiates with immense heat. Any creature that starts its turn within 10 feet of the worm takes 8 (1d10+2) Fire damage.

Multiattack. The worm makes one Bite attack and one Tail Slam attack.

Bite. Melee Attack Roll: +11, reach 10 ft. Hit: 19 (3d6 + 7) Piercing damage. If the target is a Medium or smaller creature, it has the Grappled condition (escape DC 17), and it has the Restrained condition until the grapple ends.

Tail Slam. Melee Attack Roll: +11, reach 10 ft. Hit: 13 (2d6 + 7) Bludgeoning damage.

Swallow. Strength Saving Throw: DC 17, one Medium or smaller creature Grappled by the worm (it can have up to two creatures swallowed at a time). Failure: The target is swallowed by the worm, and the Grappled condition ends. A swallowed creature has the Blinded and Restrained conditions, has Total Cover against attacks and other effects outside the worm, and takes 7 (2d6) Acid damage and 4 (1d6) Fire damage at the start of each of the worm’s turns.

If the worm takes 22 damage or more on a single turn from a creature inside it, the worm must succeed on a DC 20 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, each of which falls in a space within 5 feet of the worm and has the Prone condition. If the worm dies, any swallowed creature no longer has the Restrained condition and can escape from the corpse using 20 feet of movement, exiting Prone.