Attempting to recreate a long forgotten spell is a dangerous practice, and having an hyperactive pink pony makes your life at stake a dozen times. Twilight Sparkle had ripped a hole in her reality, and it's seemed to have altered someone's universe.
After being freed from Order's curse, the Madgod Sheogorath is left without a home. He searches the many realms of existence for a creature whose Madness rivals his own. He finds Chaos instead.
When a knight and his squire get sent to a magical world, diffrent than the one they are used to, they will have to quickly adapt and learn to over come cultural, and language, problems if they are going to get back home.
After getting letters from Celestia and Discord, Cadence decides to give a happy ending to an ancient tragedy of love. Unfortunately for her, this is the Lord of Chaos and Princess of the Sun. Also, Flurry Heart explained.
Regretting their last encounter, Sombra wishes to try to make things up to Princess Luna... but isn't the rule "once bitten, twice shy?" He has a long way to go...