Some (lightly-edited) thoughts from the very wise Chimera245, posted in the official Ironsworn Discord:
You don’t actually need any new game rules or mechanics to play a magic-user […] You can represent spellcasting completely within the existing game rules.
Throwing a Fireball or Lightning bolt at someone? That’s an attack at range. Strike or Clash + edge.
Conjuring a magic shield to intercept an enemy’s attack? Face Danger +wits.
Using a Sleep spell to sneak past the guards? That’s Compel. Summoning demons, or animating constructs to help you perform some task? Secure an Advantage.
Does your spell or ritual have a complex or dangerous ritual, which can easily go wrong? Face Danger first, to get it right.
Does your spell require some special condition to persist? (Concentration, an unbroken magic circle, direct moonlight, etc.) Makes for a good Pay the Price on a miss later.Chimera245#2857
I’ve been wondering how best to represent magic-users (and clerics) in my Dwimmermount campaign. Ironsworn has the various rituals and the devotant assets, but I felt like I might need something more. This wise advice perhaps shows that I don’t — if I just let the fiction come first, Ironsworn already has all the tools I might need.