Valheim already has its own sort of magic with the forsaken powers you get from each boss, but if you're more into to slinging fireballs around you may want to try out Skyheim. This mod adds runes that you can craft with loot from bosses and dungeons. Summon a light instead of carrying a torch. Scorch a forest full of Greylings with your fire. Oh, and teleport yourself back to your bed at will. It sounds pretty powerful, but chucking fire and ice around sure looks like a good time.
"Skyheim is a magic mod aimed at providing balanced progression and a reason to go back and slay bosses," modder "Makzimus" explains. "Each boss drops a crafting ingredient that can be used to craft and upgrade runes that will allow you to cast a variety of spells both beneficial and destructive."
Another player explains some of the particulars down here in this video on Skyheim.
I appreciate that the spells Makzimus chose all seem to mesh pretty well with Valheim's world. The first tier of skills are some expected magical fundamentals in any fantasy game: frost and fire offensive spells, a light spell, and a healing spell with an area of effect.
Tier two is a bit more about support, offering spells for stamina regeneration and staggering. The neat one in tier two though, for my money, is the warmth spell that will keep you from freezing in the mountains. You can create that rune after defeating the Elder, meaning that warmth spell will help you get up into the mountains if you haven't quite gotten around to making frost resistance meads.
Tiers three, four, and five all get into even more serious magic, from various teleportation abilities to area of effect skills for fire and ice.
Even with spell cooldowns and a mana pool, Skyheim may make you a bit too powerful in combat, especially with some of those higher tier runes. As someone who's just about to head into the plains biome though, I'm thinking I wouldn't mind being a bit overpowered right now.
You can find Skyheim over on Nexus mods to try it out for yourself.