The Princesses of Harmony (Sonic: Adventures in Equestria)

The Princesses of Harmony is the 1st episode of Season 4 of Sonic: Adventures in Equestria, and a reimagining of the Season 4 MLP: FiM Two Parter, Princess Twilight Sparkle.

Summary
When Princesses Celestia and Luna mysteriously disappear right before the Summer Sun Celebration and mysterious vines invade Ponyville and take control of Eggman's robots, the newly crowned Mane Six and Team Sonic, along with Sunset Shimmer and Discord must figure out what's going on, during all of this, the Mane Six discover the origins of the Elements of Harmony, and a old friend of Tails finally returns.

Differences

 * Applejack, Rarity, Pinkie Pie, Rainbow Dash and Fluttershy stay behind with Twilight in Canterlot due to them being princesses as well in this timeline.
 * The Mane Six all use the alicorn potion to go into the past while Team Sonic tries their best to defend Ponyville from the plundervine and Eggman's robots.

Transcript
To be added...

Recap
"Last time on Sonic Adventures in Equestria, still getting used to their new roles as alicorn princesses, the newly crowned Mane Six are surprised when Princess Celestia and Princess Luna mysteriously disappear right before the Summer Sun Celebration. As they try to figure out what happened to them, they receive word that the Everfree Forest has invaded Ponyville, if that wasn't bad enough, Team Sonic found out the these mysterious plundervines have taken control of Eggman's army, the Mane Six accuse Discord of causing the mess, but since Discord is now reformed, it couldn't have been him, if even some of the heroes still don't trust him, with help from Zecora, the Mane Six use a potion than only alicorn magic can activate, which sends them over 1,000 years to the past, where they first hand how Luna first turned into Nightmare Moon, either way, will our heroes figure out a way to stop the Plundervines from destroying Ponyville and will Celestia and Luna be found in time, find out next on Sonic Adventures in Equestria."

Trivia

 * Cosmo, who last appeared in Sonic X, makes a unexpected return to help with the plundervines.
 * Metal Sonic is shown to be immune to the plundervine's effects on Eggman's machines.