The Fey. They're many players and DM's favorite group. There's all sorts of interesting adventures that can happen when a Fey is around. If you're looking to bring more of this whimsy to your game, you can check out Professor Gilroy's Guide to Fey, a new RPG supplement that's up on Kickstarter now.
From the campaign:
The campaign's close to 2x funded, but only has 4 days left to go.