Fae

Many creatures of Faerie move between the mortal and fae worlds. Fae are immune to mystic weapons and most spells. They are vulnerable to regular iron, however, and take double damage from iron weapons (unless they have been enchanted or otherwise made mystic).   Fae generally have two levels: their level in Faerie where they are at the height of their power, and their level in the mortal world where they are weaker.