Looking back, Twilight should have known better. She really should have. Starlight wasn't all there to begin with, and it took only a few words, spoken in anger at the wrong time, to transform her into a real monster.

Now trapped in an endless time-travel hell powered by the mad unicorn's fury, Twilight must hold on to her sanity as she chases the one thing that can free her from her torment and set the world back on its path.

For the sake of her friends, she mustn't break.

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Editors, pre-readers, etc:

GuyWhoWritesThings
Applejinx
Manaphy
Queue
Majin Syeekoh
Shardikku

Reluctant Brohoof wrote most of the long summary.

The cover art is A New Villain Appears by Lukeine.