The third IDW comic mirror princess. Since she wasn't really a part of the story, incoming head canon!

Mirror Celestia's adoptive niece, bodyguard, and go-to enforcer. Both Celestias had eyes on conquering the human world, and a devastating inter-dimensional human-pony war resulted. Mirror Cadance made a name for herself by defeating Celestia Prime's captain of the guard, Shining Armor, in single combat by use of her superior cunning, deception and a healthy dose of dark magic , claiming his great sword "Mi Amore" for her own. However she soon realized it was far to large for her to wield herself and was handed a swift defeat by Luna Prime.