Since most of the good ones have already been taken, I've decided to go with sort of a "black sheep" for my choice but still one that I've come up with some good ideas for. These are the 3 prequel movies I'd like to see made for the My Little Pony Cinematic Universe.
POTENTIAL SPOILERS BELOW!!!
I. "Chaos Reigns" (Discord's Origin and Rule.)
Anyone who's seen Friendship Is Magic knows that Discord is one of the hardest characters to pin down. Little is known about where this Spirit of Chaos and Anarchy came from or even how he came to rule Equestria before Princesses Celestia and Luna used the Elements Of Harmony to turn him to stone for over a millennium. I would like to see an origin story bringing light to the unknown background of this mysterious and mischievous character and with original voice, John de Lancie, attached it would definitely be a fun ride all the way through.
II. "Star Swirl The Bearded - Equestria's 1st Great Mage."
Star Swirl The Bearded has come up in conversation numerous times in episodes of My Little Pony and even once in the Equestria Girls movie, Rainbow Rocks. Even with him being a popular topic, we still know very little about him. This movie would focus on some of his greatest feats like befriending the gargoyle, Scorpan, (resulting in Lord Tirek being banished to Tartarus) to exiling the dissent sowing Sirens from Equestria all leading up to his mysterious disappearance.
III. "An Empire Of Fear And Shadows" (King Sombra's Rise to Tyranny.)
Over a millennium ago, King Sombra ruled the Crystal Empire with an iron hoof, enslaving its inhabitants before being overthrown by Celestia and Luna. Though defeated and banished, he took the entire kingdom with him til 1,000 years later when both returned. All those who were enslaved by him fear his name. Unfortunately, in the 2-part Season 3 premiere, he's hardly given any screen time or character development before he's finally killed off. (Oh that's right. This kid's show killed off its villain) We're given a glimpse into some of the dark traps and machinations he used to prevent the Crystal Heart from being retrieved that would lead to his undoing, but the rest of the time is just a few minutes of him lingering around waiting for the Crystal Empire's defenses to go down so he can attack all while hardly saying anything. For a character like this, I'd like to see more of a backstory on him going into where he came from, how he rose to power, what was his motivation for enslaving these ponies, and how he became this terrifying figure that strikes fear into the hearts of every pony living there. The character of Sombra is actually inspired by a famous villain: Sauron from The Lord Of The Rings Trilogy. It would be nice to see Sombra given the same amount of attention as the villain he's based off of.