Which units would you replace in the Sylvan castle?

Interesting. Regarding magic, I can definitely say something about Scandinavian mythology: there was a system where runic magic was introduced by Odin (he sacrificed himself to himself, and while hanging, pierced by a spear, for nine days, he learned many things, including runes); that is, a man. However, he learned seidr, shamanic magic, from the goddess Freya. For the Vikings, everything is ambiguous.
In general, magic is probably very different among different peoples.