Remorhaz

The polar worm is a long, segmented creature on dozens of chitin-clad legs, with stubby wings on its head and neck. It is icy blue except for a white stripe along the spiky ridge of its back. It grows 3 feet per Hit Die (21 feet at 7 HD, 24 at 8 HD) and speaks only in roars and howls.

Remorhaz eat any animal flesh and will even tackle frost giants. Being slow, they lurk under snow and erupt when they hear prey, hoping to surprise it; they have 60-foot infravision. A remorhaz rears up by beating its wings, then whips forward. On a natural 20 it swallows the victim, who dies at once in the heat within. When aroused, its body generates such heat that the back spines glow cherry red: nonmagical weapons striking the back melt, and creatures touching it take 10-100 damage.

Hit location depends on position. Frontal blows against a rearing worm strike its soft belly; blows against one that is attacking hit the head unless aimed at the belly; anything else hits the body, at the DM's discretion.

Lairs are smooth, sloping tunnels through ice, snow or rock leading to a chamber twice the worm's size, or four times for a mated pair, sometimes with icy stalactites. Ice tunnels are slick because the hot back melts them and they refreeze. Hunting ranges span 60 miles and are shared with other remorhaz unless game runs out.

Prey includes deer, elk and polar bears. Pairs mate every year at summer's end and remain paired two months, yet a female produces young only three or four times over her life. She curls around her pair (or single) blue-grey eggs constantly; a minute in the cold kills them. Young start at 1 HD and reach 7 HD at four months, then leave. They have adult powers from birth but +2 AC everywhere, and bite for 2-12 at 1-3 HD or 3-18 at 4-6 HD.

Lifespan is 30 years. Eggs sell for 500 gp because the young make fine guards, though a trained worm obeys no more than one or two masters and may devour one if starving. Its heat secretion, thrym, is used in fire-related magical items and fetches 5-10 gp a flask from alchemists, with 10 flasks per Hit Die.