When Sunset Shimmer looked into the mirror it changed her in a way even Celestia never saw coming, but now Sunset can.

This Sunset is not reformed, but has seen all the crap she would have had to deal with as a princess, as a bad girl and reformed villain, and a few other possible long term futures and said screw that. She can also see a few minutes into the future with all the actions and reactions involved and plan out her moves based upon them. Sunset's power is extremely loosely based on the movie Next and book The Golden Man. She is not infallible and must actually be involved directly for 'The Mary Sue Effect' as she thinks of it to work.