An Alternate Universe were Discord revived himself a thousand years before the Mane 6 were born and battled Celestia to a draw. Story is a sort of crossover of the Slayers Anime with the MLP FIM cast playing the main roles.
Cadance feels that Shining Armor isn't understanding her feelings and needs as a mare, so she decides to teach her husband a lesson the hard way. By letting Shining experience them all first hand.