The song used is "Open Up Your Eyes" from My Little Pony: The Movie. The footage used is from My Little Pony: Tell Your Tale and My Little Pony: Make Your Mark.
The timeline video is still a work-in-progress, so I figured I'd drop this edit. Opaline is a very underrated villain and this song fits pretty well, especially with the backstory of her being rejected by Celestia and Luna. I also thought the exchange at the start between Twilight and Tempest about the former thinking they're the same and the latter disagreeing fits Sunny and Opaline's dynamic pretty well.