Ice serpent

Ice serpents were a variety of air elemental encountered in cold and snowy climates.

Description
Ice serpents had no bodies, and were instead comprised of constantly moving, ice-cold air. They were naturally invisible, but they could usually be seen thanks to snow, ice particles, and small stones that were picked-up by their windy forms as they moved.

Unlike most air elementals, ice serpents could not fly, and instead moved forward by propelling themselves along the ground, giving the appearance of writhing and slithering.

Combat
Ice serpents attacked by wrapping themselves around a target, but instead of constricting as a physical snake would, they instead drained the heat from their prey. Their victims would begin to go numb from the cold, and ultimately fall unconscious as the serpent proceeded to drain the last of their vital heat.

As creatures of pure cold air, they were difficult to injure with mundane weapons and were fully immune to any magic that relied on ice or cold, although they were highly susceptible to fire.

Ecology
Ice serpents fed upon the body heat of living creatures, which they hunted in snowy regions. During the mid-to-late 14 century DR, they were known to inhabit the Sea of Moving Ice and the North as far south and east as the Trollmoors, although they were known to range further south during the cold winter months.

History
These elementals first appeared in Faerûn in the mid-to-late 14 century DR, and were thought to have been summoned by an evil cleric of Akadi who dwelt near the Ice Lakes in the Frozenfar.