Derpy is, like most unnecessarily pleasant ponies, hiding something. The truth is she's Ponyville's resident agent, toughfilly, and all-round badass. She's dedicated to battling the Effects, monsters from Celestia-knows-where. All the while she tries to keep the Ponyville residents thinking she's the slightly-thick mailpony.

Thanks to Dragonbeak of Deviantart for letting me use her art as the cover. The non-clumsily-butchered piece is here: http://dragonbeak.deviantart.com/art/Where-s-Derpy-259340056