My Little Pony: Rainbow Roadtrip, on Discovery Family
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Caution: spoilers.

This aired during the midseason break of My Little Pony: Friendship Is Magic season 9. Rainbow Dash receives an invitation to be the guest of honor at the annual Rainbow Festival in a town called Hope Hollow. So she and the rest of the Mane 6 pile into a hot air balloon and set off. Eventually they crash into a giant rainbow billboard, which wrecks their balloon as well as the billboard. They manage to get to the ground safely, and find that they've arrived in Hope Hollow. Everything looks pretty gray, though that could just be because it's twilight. (I was going to say "no pun intended," but then I realized it might be more apt to say "dusk," and decided to go with "twilight" anyway, for pun's sake.) Anyway, they meet a pony named Petunia Petals, who runs the only hotel in town (among her many other jobs). It only has one room, and it's in pretty bad shape.

The next day, the town is just as gray as before (if not as dark), and all the residents of Hope Hollow are also devoid of color. They finally meet the mayor, Sunny Skies, who had invited Rainbow Dash for the festival. He takes them on a most unimpressive (but somewhat amusing) tour, before finally admitting (via song) that they haven't had a Rainbow Festival in some years. The town used to be full of color, and the festival was presided over by his grandfather, then his father, then Sunny Skies himself. But he apparently added too much magic (or maybe the wrong sort of magic) to the rainbow generator his grandfather had invented, and when he turned it on at the last festival, it exploded and drained all the color from Hope Hollow. Actually, even before that, most of the ponies in town had become less interested than they used to be in social interaction, and this catastrophe just exacerbated their recent tendency toward being antisocial. Sunny had hoped inviting a celebrity Wonderbolt like Rainbow Dash would make ponies regain an interest in the Rainbow Festival. And of course, all of the Mane 6 agree to do whatever they can to help. In particular, Twilight Sparkle wants to figure out a spell to bring color back to the town.

I want to mention that throughout the special, it's obvious that Sunny Skies and Petunia Petals have romantic feelings for each other, but they're both too shy to tell each other how they feel (and seem oblivious of each other's feelings). Anyway, while Twilight goes to the library (where Petunia works as librarian) to research magic spells, her friends split up to make preparations for the festival. Um... while most of the town's ponies have Minnesota-like accents, Pinkie and Fluttershy meet a couple named Mr. and Mrs. Hoofington, who had moved there from Manehattan, and have more sort of "lockjaw" accents. They're bakers, but they've been having trouble since the color disappeared from town. I don't want to spoil any details, but Fluttershy finds a way to help them with their baking for the festival, along with their neighbor, Moody Root. Meanwhile, a pony named Torque Wrench had been fixing the crashed balloon, and now Applejack gets her help in fixing up the crashed billboard. Rainbow Dash meets a couple of young fans of hers, brother and sister pegasi named Pickle and Barley Barrel. She gives them flying lessons, so the three of them can perform together at the festival. And Rarity meets Kerfuffle, who owns a boutique, as well as designing alterations to clothes that were designed by other ponies (such as Rarity herself). Rarity encourages Kerfuffle to have more faith in her (Kerfuffle's) own designs, as well as getting her help in making fashion accessories and decorations for the festival. While all this is going on, Sunny Skies mainly focuses on writing a speech, about which he's very nervous.

Well, there is eventually a plot twist, which was pretty predictable. (I mean, there are obvious hints throughout the events leading up to the festival.) But of course everything works out, in the end. Color returns to the town, ponies start being social again, and... another very special development occurs. It's all fun and amusing and sweet and basically everything you would expect from the MLP:FIM franchise (including a few decent songs).

Immediately after the special, Discovery Family aired two animated shorts, "The Craft of Cookies" and "Camping Must-Haves," which are both from season 2 of the Equestria Girls webseries "Better Together" (which I haven't seen yet).