Sunset Shimmer

Starting out as a villain Sunset shimmer stole the element of magic from twilight sparkle in order to use it's power to enslave her schoolmates and invade Equestia. She proved herself to be very good at being very bad. Framing Twilight for crimes she hadn't committed and almost getting her kicked out.

On her first day no less. If it wasn't for Twilight's bond with the element Sunset might have won. But that defeat proved to be the best thing for her. Humbled Sunset began opening her heart to her new friends. They welcomed her with open arms despite the fact that she used to bully them.

Not something that could be said about the rest of the school. But after fighting off the Sirens and then reforming their worlds Twilight Sparkles (Sci-Twi) next to no one could deny that she had earned her place among her fellow students. Not that a few of them still didn't hold a grudge.