Also if you have ideas on a suitable mechanic/effect for it that would be cool :) I'm not too knowledgeable in fairies. But considering they're into magic and such it should suit a bunch of effects.
It certainly should be a terrain. A bunch of effects that would suggest trickery or randomness would work, my first idea was "when a building is placed nearby, give -3 if it has an uneven number or +1 if it is even)"
