Story:
Everchange Spectical, a 20 or so year old Earth Stallion, walks among the populous of Ponyville, but everyone is in a fuss, and some just outright don't like him. This is due to his unique ability to transform into creatures, 10 of them, exactly. He's a rather odd stallion, but he seems to have a personal grudge against Celestia, but why? Not to mention he has a real bitter opinion of Twilight. As things in Ponyville finally come to calm start for peace, after what happened with the Mane 6's cutie marks being swapped around, and dealing with the likes of Discord, Everchange has tried to be a bit more open with his abilities, but this would cause a problem with a secret organization, who seems to be against the stallion's efforts to change, and use his abilities to help other ponies.
With a bit of help from his friends, he'll brave through extraterrestrial monsters, equestrian beasts, and soon, he'll be ready to personally meet with Celestia, to finally thin the bad blood between them.

(Here's a link to the rebooted/rewritten version of this story. It's gonna be very different, but that's fine. This is A Stallion of many Shapes and Sizes)