Hellworms
From The Fifth City Wiki
"Hellworms. One must admire the advertising enterprise of giving them such a name."[1]
Hellworms are serpentine creatures that originate from the lands of Hell. These creatures have law-furnaces within their bodies, and they're capable of chewing tunnels through even the most impassable of cliffs, leaving behind molten rock in their wake.[2] They're also useful for mining and processing certain rare ores and metals, even ones that don't strictly exist.[3]
Hellworms are reared by certain devils of Hell,[4] who use Nevercold Brass bridles to direct and secure them properly.[2] However, they can be extremely dangerous to handle without proper training, as would be expected of such a powerful creature.[2] </gallery>