Frost vrykul

Frost vrykul are a variant of vrykul. They look like vrykul, except their skin is blue and layered with frost. Frost vrykul may be a race, but they are not unified, and may not even be related.

Factions
Two major populations of frost vrykul are known to exist:

Hyldnir
The hyldnir are an entirely female population of frost vrykul, located in the Storm Peaks. They inhabit Sifreldar Village, Brunnhildar Village, and Valkyrion.

Brunnhildar Village is located in the eastern area of the Storm Peaks, and the vrykul there retain their ancestral loyalty to Thorim. They seem to despise males of every race. With females they seem to be more merciful. Captured males are either put to death or enslaved, regardless whether or not they're vrykul.

Members of this population compete against each other in the Hyldsmeet, the winner of which is entitled to an "audience" with. It is unknown what happens to those that fail the Hyldsmeet. They are particularly opposed to the frost vrykul of Valkyrion, whom they consider traitors for allying with the Lich King.

In Valkyrion, located in the western area of the Storm Peaks, the hyldnir there are loyal to the Lich King. They hope to "accept the Lich King's gift" and be transformed into val'kyr. Those who are judged worthy here by the Lich King will become val'kyr. Also present in the village is a breeding area for Blighted Proto-Drakes.

Ymirjar
Located in central Icecrown, Ymirheim is populated by both male and female frost vrykul. This population, called the Ymirjar, are undead and allied with the Lich King. These were vrykul who traveled to Jotunheim and fought at Valhalas. The winners of this competition are taken to Ymirheim and become Ymirjar. The losers become vargul.

Unlike many of the Lich King's minions, the frost vrykul appear to retain their intelligence and free will, serving their master of their own volition in the hopes of gaining the Lich King's favor and being turned into higher order undead. Vargul are a more standard form of undead.

It is unknown if all, or any, ymirjar were frost vrykul to begin with, or gain that form upon undeath. Non-frost vrykul, such as Halfdan the Ice-Hearted, are "judged" by the val'kyr, but are not shown to change into anything.

Though the ymirjar seem to serve the Lich King exclusively, the hyldnir serve Thorim and believe those live in Valkyrion are traitors. It is unknown what the hyldnir think of the ymirjar.