Discord is the spirit of disharmony. His was turned to stone by princess luna and princess celestia, only to be awaken by two arguing fillies (young ponys). He does things like turn the ground into a checker pattern or makes houses one sided and knocks them down. he also "hypnotizes" Rainbow Dash, Rarity, Fluttershy, Applejack, and Pinkie Pie into the oposite behavior. I won't say anymore for bronys who haven't got the this episode or any episode after.