After Tirek's defeat, Twilight is reminded of Rarity's magical mess in "Inspiration Manifestation" and gets worried about the possibility of there being more dangerous spell books in the Castle of the Royal Pony Sisters. When exploring it alone, she comes across Molly, the sum total of all Celestia's severed kinks and desires, who turns out to be very persuasive.

Twilight agrees to a deal with the spirit: Allow Molly to experience life though proxy in exchange for all the goddess' knowledge and power.

What happens next is entirely expected.

Proofreading and cover art by: The Exotic Natasha
Proofreading by: iakovl
Editing by: Jake The Army Guy and habitual
Original Idea from: DarknessRising