A Frost-Wyrm is a legless serpent as long as a river barge, thick as a horse’s barrel. Its hide is plated with frost the grey-white of the cinder it moves through, and blue fire shows in the seams between the plates and in its wide, lidless eyes. Its jaws are toothless, edged with hard rime. When it rises from the cinder, grey dust pours off it like water.

It moves slowly when it hunts, pushing through the cinder like a plough below the surface, and very fast at the last. The hiss of the Fields deepens around it to a long, low crackle, and the cold near it is enough to frost an eyelash.

They live only in the larger, older fields, lying buried in the deep cinder near the great blue fires. A field holds few of them, often one, and harvesters learn where it sleeps.

A Frost-Wyrm waits under the cinder for warmth to pass over it, then rises and coils. It does not crush; its touch alone drains, and a creature caught in its coils freezes where it stands, its face locked in surprise. It leaves the frozen body where it fell and moves on, which is why the Fields are full of statues. It is drawn to groups and to fires, and a careless camp can bring one from far across the field.

It drains heat faster than anything else in the Fields, through touch and through the air close around it. Its frost plates turn blades, and fire set against it is consumed as all fire is there.

Frost-Wyrms are thought to be very old Cold-Salamanders grown huge in a long-lived field, though no one has watched one grow. They seem to live as long as the field does. A dead one leaves a long ridge of rime and glassy cinder.

Its frost plates, prised from a carcass, are prized as the coldest thing a smith can carry out of the Fields, used to quench metals that must resist heat. It is deadly to anything warm, and the only defence harvesters trust is not to be there when it wakes.

Tales from the Fields' edge make the Frost-Wyrm the fire’s own body, the awareness some believe the fire has, coiled in the cinder. It is a beast, though no one can say what the fire is. People of volcanic country call any long, sudden cold in the year a wyrm’s breath.

Volcano-country hunters swear by the beast-hunter who went into the deepest field after a wyrm that had taken his son, and came back frost-blind with its fang, which hangs in a volcano-country shrine to this day.