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

Fiery Blood. When the abyssal worm takes more than 50 nonmagical damage during an attack, it will bleed. It's blood will splash a 5 ft. radius around the wound. If something is touching the blood, deal it [2d6+5] fire damage.

Devour. 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) fire damage at the start of each of the worm's turns.

If the worm takes 70 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.