This movie aired around the time Friendship Is Magic was halfway into it's final season. Even after 2 years, it's still one of my favorite material from the 4th generation of MLP. Characters like Petunia Petals, Kerfuffle, Torque Wrench, Barley and Pickle Barrel, Mr. and Mrs. Hoofington, and Moody Root will remain as the final additional characters of Friendship Is Magic. Along with Hope Hollow being the final location that hasn't been discovered until this film came out.

Some say this is a sequel towards the 2017 movie but for me, it's more then that, it was one of the final gifts of the show's quality before it all came to an end.

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It's outstanding in its quality and it feels the same way to me, one last, big gift before the show races up to its finish line. With an intriguing, mysterious plot that contains more than is shown on the surface and that invites you to take a deeper look at everything that is happening. I should watch it again today and I hope that the occasion will inspire some pony authors to write for it. Barley and Pickle need more stories.
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Characters like Petunia Petals, Kerfuffle, Torque Wrench, Barley and Pickle Barrel, Mr. and Mrs. Hoofington, and Moody Root will remain as the final additional characters of Friendship Is Magic.

However, as much as I love "Rainbow Roadtrip" and the citizens of Hope Hollow, they aren't the final, new cast members of the show. After them, we still met Sans Smirk, Fire Flare, Feather Flatterfly, Hot Streak, Night Fire, Spur, Biscuit and Luster Dawn. They aren't being seen in "Rainbow Roadtrip, but you shouldn't forget about them by calling the ponies from Hope Hollow the "final additional characters of Friendship is Magic".

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Sorry, I barely write a lot to remember most of the characters of FiM.