Season three with thirteen episodes should be released in October
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According Equestria Daily one the releases of a MLP toy showed the image of a new pony which many people believe to be the new villain.
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According to the toy box set for Princess Cadance and Shining Armor they both rule The Crystal Empire together. Another toy release of Princess Skyla suggest that the two newlyweds have a child.
First two episodes called The Crystal Empire
The Crystal Empire Part 1 overview (IMDb version)
A new land has appeared in the cold north of Equestria, and Twilight and her friends need to find a way to protect it. Her friends try to occupy the Crystal Ponies at the Crystal Fair, Twilight searches for the hidden Crystal Heart that is key to the empire's safety.
The Crystal Empire Part 1 overview (Wiki version)
A magical empire has suddenly appeared in the arctic north of Equestria, and Princess Celestia needs Twilight Sparkle and her friends to find a way to protect it. While her friends try to keep the Crystal Ponies occupied at the Crystal Fair, Twilight Sparkle searches for the hidden Crystal Heart that is the key to keeping their empire safe from harm.
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There are confirmed two songs "The Failure Song" and "The Ballad of the Crystal Ponies"
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Princess Cadance is mentioned in the "The Ballad of the Crystal Ponies" and appears on the DVD case of an upcoming release called Adventures in the Crystal Empire
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If you watch the Comic Con Panel it seems that they give some hints along the way.
Tabitha St. Germain (voice of Rarity) comments in her liking Fluttershy become a dragon. 21:20 in video
Cathy Weseluck (voice of Spike) comments on maybe Octavia having a duet with Rarity. 28:44 in video
The return of Discord and Trixie is also very probable.
Derpy talking may not happen this season, but she probably will in upcoming seasons.
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