5e SRD:Purple Worm
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Gargantuan monstrosity, unaligned
Tunneler. The worm can burrow through solid rock at half its burrow speed and leaves a 10-foot-diameter tunnel in its wake.
Multiattack. The worm makes two attacks: one with its bite and one with its stinger.
Bite. Melee Weapon Attack: +9 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.
Stinger. Melee Weapon Attack: +9 to hit, reach 10 ft., one creature. Hit: 19 (3d6 + 9) piercing damage, and the target must make a DC 19 Constitution saving throw, taking 42 (12d6) poison damage on a failed save, or half as much damage on a successful one.
The massive monster known as the purple worm terrorizes the creatures of the Underdark as it chews through solid rock in pursuit of prey. A dim-witted, ravenous force of nature, this creature regards anything it encounters as food.
Ravenous Hunters. Loud noise attracts purple worms, which have been known to interrupt underground battles and tear through subterranean cities seeking prey. The underground civilizations of the drow, the duergar, and the mind flayers maintain special wards around their settlements to deter these monsters.
Boons of the Worm. When a purple worm burrows through the ground, it consumes earth and rock, which it breaks down and constantly excretes. Precious metals and gems can thus be found within the bodies of purple worms, which are targeted by particularly brave and foolhardy treasure hunters.