It's clear in the purgatorial realm of Valheim that there's a good bit of magic in the game. However, you'll generally be limited to the weapons and armor most Vikings would be able to make. A newly-released mod changes that by letting your character take up the dark powers of necromancy and lead the undead into battle.
Created and released today by "flippyflip3," the Necromancy mod adds the namesake magic into the game through an item called the Convoking Wand. By using this item, players can summon up to eight skeletal minions as well as teleporting them to the player, executing one to heal others nearby, and heal them without sacrificing one of their own. Of course, messing with such dark powers comes with a price, and using the Convoking Wand saps health instead of stamina. This thematically-appropriate bit of balance is meant punish players who try to get into melee and also use summons, since most summoners are the type to hide behind their minions.
So far there are only two types of creatures players can summon. Warrior skeletons are capable of blocking attacks while archer skeletons are deadshots who can often tag running deer or flying deathsquitos. These two types are best combined together as the warriors will always stand in front of their archer allies and help hold up enemies. Flippyflip3 is planning to add in more customization to weapons and skills as well as new creatures, noting that adding more creatures is "a lot more involved than you'd think."