Dark Qiviut

Four words: best villain so far.

And her motivation was a part of the reason why. She manipulates others to gain their trust and become close confidants. She became a very close, trustworthy student in Twilight's school, because she used those lessons to achieve and earn status; she was Twilight's best student. When Equestria's losing all its magic, they'll go to her for guidance and comfort. Her plan is to lead a mob to overthrow Equestrian royalty, who are openly vulnerable without magic to protect, defend, and lead.