Siege Monster. The dune wurm deals double damage to objects and structures.

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

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 28 (4d12 + 5) piercing damage. If the target is a Medium or smaller creature, it must succeed on a DC 16 Dexterity saving throw or be swallowed by the dune wurm. A swallowed creature is blinded and restrained, has total cover against attacks and other effects outside the dune wurm, and takes 17 (5d6) acid damage at the start of each of the dune wurm’s turns.

If the dune wurm takes 20 damage or more on a single turn from a creature inside it, the dune wurm must succeed on a DC 20 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 dune wurm. If the dune wurm dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 15 feet of movement, exiting prone.

Acidic Bile (Recharge 6). The dune wurm expels a spray of acidic bile in a 60-foot line. Each creature in that area must make a DC 16 Dexterity saving throw. On a failed save, the creature takes 22 (4d10) acid damage. On a successful save, the creature takes half as much damage.