This story comes in two parts: The Nightmare Chronicles and The Nightmare Chronicles: Rapture. Rapture is filled with mature content so I am submitting them seperately.
In TNC, Nightmare Moon is brought back by the Moonmare Apprentice she created. Upon her arrival NM banishes several ponies to Alquestria. Which is the distant world Alicorns came from. Everything Alquestria related is covered in Rapture.
The plot thickens, Nightmare Moon And Tyrant Celestia (who is pink not white btws) have been working in concert for 1000 years to take over complete power from the True Princesses. The Tyrant as a disembodied spirit has been manipulating celestia all this time, successfully obtaining the knowledge needed to harness the power of the elements of harmony via the friendship reports.
At this point I have 3-4 conflicting plot twists. Havent decided yet. And to acctualy get here i have a buck load of Writing to do. So thats what I got for now.