This is Mastermare, one of my first ever OCs. I created her for the same “fan series that never happened” that the Mane 6 Cool Gear were created for. I needed a villain for the potential series, and at the time I was starting to construct the series (around Seasons 5-6), I didn’t like the options for villains I could have used. So I made my own.
 
Mastermare is the last survivor of the kingdom of Codexia, a technologically advanced pony-inhabited land. She was born in a family of villains, but after losing her parents during an assassination attempt on the Codexian queen, and her horn in her subsequent trial, she bombed the city and traveled abroad.
 
From then on she worked as a mercenary-for-hire, hoping her employers could lead her to a city or kingdom that she could conquer. Eventually, her travels led her to Equestria, where she offered her services to Queen Chrysalis, who she betrayed later on to conquer Equestria herself.
 
Mastermare has a rare gift - two cutie marks, both inherited from her parents. She has the extreme fighting skills of her father, and the high-level technological intellect of her mother. She also has endless amounts of Codexian technology at her disposal, which she constructs into weapons, vehicles, robots and sentries, and upgrades to herself, including her cybernetic hooves with retractable fingers, and her helmet to replace her horn.
 
Mastermare is extremely ambitious and stops at nothing to get what she wants. She never trusts anyone, and never lets herself get attached to anyone, as that once cost her a friend/partner.