Ice Serpent

Beyond the normal dangers of Faerûn's freezing North, a winding invisible predator is found. What seems at first to be the work of some twisting unnatural wind working itself over the snow and rocks is something else. Soon you find yourself trapped in the cold coils of a cruel unseen something, squeezing your bones and soaking up your life-heat. Something thin, quick and frigid tickles your cheek.

It's difficult to find a creature to go under the elemental tag that'll be interesting. Most of them are X Elemental or Y Elemental, while the more interesting ones get filed under the outsider type. The Ice Serpent is something that managed to slip through the gaps of that classification hoo-ha.

This creature has an interesting way of dealing damage. It's pretty simple in its attacks, being mostly a creature that grabs and squeezes, lacking even a bite or slam attack. It's constrict deals a combination of lethal damage (the constriction itself) and nonlethal damage (cold damage as it drains the heat from you). Potentially, it can just suck the heat out of you until you're unconscious then slither off. And then a blizzard kills you. Them's the breaks.

Also a little bit strange that despite the fact that this creature subsits on the body heat of living things, it still takes double damage from fire sources (it has the cold subtype). I guess something has to balance out the absurd DR it has.