You finally... won.
MLPEG.
(You are Sunset Shimmer.)
You are Sunset Shimmer. You used to be a student of Princess Celestia, the ruler of Equestria. You were a good student and achieved good results. At some point, you became too ambitious and wanted more. You wanted more power and didn't want to continue studying, but when you were rejected, you fled to another world and dropped out.
After arriving in another world, you transformed from a pony into a human. In this world, everyone was human. You quickly got used to your new body and settled in well. You found your home in this world and began attending Canterlot High School. At first, you were quiet and calm, but then your temper began to show and quickly became the biggest bully in school.
At school, everyone began to fear you. You even had your own minions, but you still dreamed of power, even though you knew you needed a plan.
At some point, when you used the portal to Equestria (which was a statue near the school, but which no one but you knew about) to get back to Equestria, you learned that the coronation of a new princess, Twilight Sparkle, was about to take place. It turned out that this Twilight was Princess Celestia's new student, but she was clearly not like you.
You learned that Twilight's crown was one of the Elements of Harmony, which could grant you the power you desired, and you decided to steal Twilight's crown. Unfortunately, while stealing the crown, Twilight herself spotted you, and a chase ensued, but you eventually escaped with the crown through the portal.
Twilight immediately chased after you, but she was completely unfamiliar with this world, unlike you. To get the crown back, Twilight had to participate in the Fall Formal Princess Contest, and most importantly, she had to fight you. You were confident you'd win, but Twilight, with the help of her friends from this world, prevailed. Twilight became the Fall Formal Princess, and therefore, received the crown.
You were angry and weren't going to let Twilight go that easily. You lured Twilight out of school and threatened her that if she didn't give you the crown, you'd break the portal, and she wouldn't be able to return to Equestria. Of course, you didn't mean to break the portal, because you'd need it later. You hoped you could force Twilight to surrender.
But then again, things didn't go as planned, and then you decided to take the crown from Twilight by force. You started fighting her, and during the fight, the crown fell off. You reached for it first and grabbed it. You couldn't believe you'd finally won. Twilight, noticing the crown in your hands, looked frightened.
Twilight knew that using the Element of Harmony the way you planned to use it was dangerous. Twilight and her friends tried to dissuade you, saying it was dangerous, especially for yourself, but you weren't going to listen to them; you were sure they were just lying, trying to talk you into it.