Muspelir
Midgir touched by the ethereal head-fires of Musple.
The sorcerous powers of arcane fire course through their very beings. With its mastery over the Bifrost, the Aesir government has been able to shape these powerful casters into potent weapons of its wars, both internal and external.
However, it is just as often that these sorcerers have turned to lead some of the most devastating rebellions that the Aesir have suffered. When left to their own devices, Muspelir are more likely entered into pacts with Bifrost beings from Muspel. Most notably, an ancient but bellicose entity named Surtr.
Niflir
Midgir touched by the ethereal melt-off of Nifle.
The crushing might of arcane water flows through their very beings. As with the Muspelir, Niflir have also been used as powerful agents of the Aesir.
However, whether it is due to there relatively increased rarity, or perhaps due to their literally cooler nature, they are less likely to develop innate sorcerous abilities. Rather, they are most receptive to tome Ethereal Magic gained by repeated practice and pacts.
As opposed to the Muspelir’s rebellious streak, Niflie are more likely to simply go AWOL. Many have been seen among the ranks of the Jotunn. A common link between the Jotunn and the Niflir is thought to be the worship of a martyred Bifrost entity of Nifle, known as Ymir.
Lindwir
Midgir touched by the primordial elements of World Trees.
The natural magic of Real-Space burrows through their very beings. As opposed to either the Niflir and Muspelir, the Lindwir wield Primordial magic, the real-space counterpart to the Arcane and Divine magics of the Bifrost.
Due to the highly monitored nature of Primordial Magic, the Aesir government goes to great lengths to emphasize its control of, and benevolent leadership over, their Lindwir population. This in turn has made Lindwir some of the most fanatically loyal of the abnormal Midgir mutants.
Lindwir raised, or coaxed away from the influence of the Aesir generally attempt to remain hidden. Eventually, it seems that these renegade Lindwir inevitably end up worshiping real-space magic. A central figure in this worship is a World Tree entity known as Nídhogg, who bears a striking resemblance to a great serpent depicted in the Cult of Ragnarok
