I had an idea once .at first the main character would be a human in equestria but after all the stares he got he would ask Twilight to turn him into a pony. The younger the beter since he would expect going from biped to quadruped would cause him to have to learn how to walk. But while thinking about it he would come up with an idea to make the Situation more interesting with a bet.

If Twilight wouldn't be able to take care of his infant self without help then she would be turned into a foal for a month where she would get babied by the princesses. (Ps: I thought that it would be funny that the gala would be during that month)
If she can do it then at first he tried to make it that she could decide when he would become an adult again but from his tone she would realize that he truthfully wouldn't care about how long it would take so instead she said that instead of a colt she would turn him into a filly.

During the challenge I would have made the readers vote on who would win the bet and that would be the first vote.

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(Couldn't fit the entire idea in one post.)
Another thing he would be worried about would be his memories. He wouldn't be sure that his infant brain would be able to retain the memories so he asked to store them externally in a locket that Twilight would have given to princess Celestia for safekeeping. After the whole Discord thing where I would have taken suggestions on what Discord would do to mess with our main character. The wedding would come along where the second vote would come along.

During the fight between Celestia and Chryssalis the bug would notice how protective the princess was of the locket and wanted to know why so after beating her and before the barrier would throw her out of Canterlot she would grab it.

The vote is would the force of the barrier hitting her be enough to make her drop the locket:

Anyway while I can get idea's once in a while I don't really know how to write out the details so I just decided to share the premise here. So if anyone wants to take this story idea they have my permission.

Thought of a third vote:
During the return of the crystal empire would Twilight's parents be able to foalsit:
Yes. (Warning there might still be some changeling stragglers in Canterlot and a foal that close to the student of the princess would be a very good target to replace) (AKA a stealth section featuring nightlight and velvet trying to sneak to the castle while disguised changelings are trying to track them down)
No. (Warning Sombra would realize that a foal that close to the ones trying to stop him would make for an excellent hostage.)