how deal with etherial enemies?

[Jasper]

Phantasmal battle summonings all have magic attacks, although this is offset by allowing a MR save. Hama Dryads have Strength stealing (also with a MR save) although they're hard to get much use out of. A summoned commander can use magic weapons.

Some factions also start with troops wielding magic weapons. Caelum and C'tis spring to mind. I would guess the damage from a Fire 9 blessing is also magic, though I haven't checked.