Twilight on a trip to the canterlot library, finds a black mysterious book in Princess Celestia's personal stash. Curious of the book, she decides to take with her to read. However when she returns back to her home in Ponyville, she finds out the dark secrets that the book holds and even finds a new spell to cast. For a moment the spell did not work so she thought it was useless to her, she leaves the book closed on the table and leaves to go for her friends. Once she had returned with her friends she decides to practice the spell one more time, this time her effort paid off. The only question remains 'Was it worth it'
(due to the name change i had to take it off and change a few things)