When the Elements of Harmony get into a heated argument about who has the hardest life and who could do each other's jobs better, fate decides to make things interesting...
Rarity and Pinkie Pie both seem to need something from the Everfree forest, and so they decide to find what they both need together. However, they both accidentally unlock some dark magic and major changes happen. They switch bodies.
After Twilight gets her Castle, she tries a spell that she had come across paths with. While in Canterlot, Princess Celestia and Princess Luna found the same spell.
Applejack, Trixie, Golden Harvest and Fleur de Lis find themselves switching bodies. As they each face this new situation in their own ways, the race begins to find the artifact responsible and go back to normal... before it's too late.
Sweetie Belle magically derails a science experiment, causing her to switch bodies with Rainbow Dash. They try to masquerade as each other, but the weather team needs help and Diamond Tiara, well, is Diamond Tiara.
Twilight Sparkle has a new spell. Rainbow Dash doesn't know what it is but with everypony acting out of their minds she's the only who can figure it out.
Celestia is having a horrible recurring nightmare. She knows that this dream is ridiculous and irrational. She knows she can trust Luna, there must be someway to rid herself of the dream. There just has to be a way!
Rainbow Dash wants to see what it's like to be a Dragon, Spike wants to be a pony to impress Rarity. Twilight just wants some peace and quiet, so she grants their wish.