An alternative ending/consequences of what happens if.
Per Example: What If...Twilight refused to stay on Ponyville?. Something like that I think you catch the idea, right?
Off-Topic:
Update 1/12/2018: 'Queen Chrysalis realized her great goal.', this chapter was edited due to a misunderstanding from my part.
Update 29/12/2018: Storybook status changed to 'on hiatus'.
Update 2/1/2019: Storybook status changed to 'Incomplete'.