Starlight Glimmer

Starlight Glimmer is a unicorn who is very talented at magic, like Twilight. She first appeared in season five's two-part premiere "The Cutie Map", when she was the founder and leader of a village where she wishes to build a "perfectly equal society" by magically removing other ponies' cutie marks because she believes differences cause disharmony between friends, until Twilight and her friends came to her village and ruined everything she built. She returns in the season's two-part finale, "The Cutie Re-Mark" to get revenge on Twilight and her friends by time traveling back to the past and prevent their friendship from happening by stopping Rainbow Dash from performing her first Sonic Rainboom. Twilight and Spike followed after her, but they get trapped in a time loop as they repeatedly fail to stop her from altering the past. When they tried to show her how her actions are ravaging Equestria, Starlight refuses to believe them and shows them how she was separated from her friend Sunburst, the day he earned his cutie mark and to study magic in Canterlot, which sent her down her villainous path. But Twilight convinced Starlight to change her ways and make new friends, and even takes her on as her student. In season six, Starlight starts learning about friendship as Twilight's student, until she graduates in season seven, after defeating Queen Chrysalis and bringing harmony to the Changeling Kingdom. In season eight, she becomes the School of Friendship's guidance counselor to help the students with their problems. Later in season nine's twentieth episode, "A Horse Shoe-In", she becomes the school's new headmare as Twilight was leaving to rule Equestria.