the Dresden Files-Twin Cities
The Fairy Courts
The fairy courts make up the majority of random creatures that leak from the nevernever into our world, including goblins, trolls, elves, nyphs, dryads, satyrs, fauns, gnomes, and hundreds more. Most fall into one of three courts (below) but all have certain universal traits. Iron, or any alloy containing iron, burns them like fire. They are bound by the terms of any bargain struck with them, and will in turn hold mortals accountable to their end. Exchanging gifts with a fairy is dangerous, and accepting one with nothing given in return constitutes an open bargain, the terms of which the fairy will fill in on their own. They cannot lie, though they are by no means compelled to tell the whole truth. The machinations of the fairy courts can impact the mortal world, causing ice ages or global warming, storms, pestilences, and other calamities.