Well, kinda need a magic system for the Alfar to work. So better put it here, so I can easily refer to it when I make them.
Seidr
Seidr is a magic of nature and spirits. Practiced by either spirits (Alfar are nature spirits) or those in tune with the spirits.
Seidr has a focus on place or people. Enchanting an area of land or cursing a man with undeath.
On a man, Seidr can do almost anything on their body, but it's effect on the mind and soul is weak in comparison.
People can even sustain their bodies with Seidr, achieving immortality. Though this is easier said than done. And you need to replace the aged flesh.
They can also cure any ailment that may affect the body, with enough practice.
Of the mind, one can cause visions and knowledge, but not control. While one may gain knowledge from another, they cannot gain memories.
It's easier to learn an entire language from someone with Seidr, than it is to learn a single recipe for food.
Though one can learn a lot about the world itself with Seidr, like the state of the land, what ails a person or animal may have, or what caves lie nearby.
Of the soul, one can grant slight separation of body and soul. Even make a Vardøgr, a sight of one before they arrive, like a reverse deja vu.
Skilled practitioners can even make the Vardøgr act as a messenger, or go to places out of reach.
But Seidr can also be used to curse people, send souls to different afterlives, bind a soul to the world, making them walk the world even when dead.
But as long as the person is alive, they can never remove their soul completely, they can never hurt a soul either.
Even capturing a soul is impossible, they can only prevent it from leaving it's body (or a certain place).
Seidr can be warded off by cold iron. Even an amulet of cold iron will protect you from any curse they may cast, even expel the curse if you're afflicted (though it may take time).
Cold iron is iron that has not been melted. Though iron may become cold iron after being melted, it takes centuries to do so. Though if it's steel, it'll take millennia instead.
Cold iron will ward against Seidr over 5-100 meters (depending on size), so one can ward with an amulet, or hiding in the mountains.
Seidr can also be used to enchant nature itself. Make plants or animals live a thousand years, grant shapeshifting into ferocious beasts, and enchant a land so other spirits will be born.
One may even command nature itself with Seidr, pacify beasts, call them to aid you, even cause roots to grab your enemies.
Though one must never underestimate the nature while doing so. Because if nature is angry at you, it'll attack you more fiercely than any human ever would.