All facts provided by Xannot
- Both Discord and his voice actor (John de Lancie) are confirmed to return in season 3.
- Whenever Discord teleports or makes things disappear, stars appear.
- Whenever Discord hypnotized one of the mane 6, stars appeared in the background.
- When Discord hypnotized Rainbow Dash, silhouette of the maze was shown with its center being a swirl.
- Both Discord and Star Swirl have a white beard.
- Cheerilee said Discord has a pony head, so draconequii seem to be closely related to ponies.
- Discord is able to time travel, and time travel spells are kept in wing named after Star Swirl.
- There is a huge hourglass in said library wing that seems to be counting to something important. Twilight was easily let inside by a guard, so maybe Celestia wanted her to learn the time travel spell?
- Celestia has prepared next level of Twilight's studies, and Luna's book with stars and a swirl appears in the same 2-parter. Markings from this book also appear on the tower on sharp left during The Failure Song. What if Twilight is supposed to study under Star Swirl?
- Amniomorphic spell may actually be Omniomorphic, which supposedly would transform things. Star Swirl is its inventor, and Discord looks like a product of multiple unsuccessful transformations.
- Discord's theater seats have stars on the edges.
- Star Swirl lived at the same period as Clover the Clever (he was mentioned in Hearth's Warming Eve), and both Discord and regal sisters seem to appear shortly after Equestria's founding. Discord clearly remembers Celestia, and even seems to know her personality ("I forgot how boring you can be, Celestia"), which implies he had spent quite a bit of time with her in the past.
Does this fit in with the my little pony season 3 finale?