In the alternate timeline where Sombra was not stopped, a human finds himself suddenly in Sombra's body... just after the dread tyrant has conquered Equestria.
Leon always had a lot of adventurous dreams in his life, but none of them could quite match this one. Being in the role of a unicorn villain, in a mysteriously well detailed world, in which he has to take over an entire empire!
In an Equestria where Celestia and Luna have slain each other, a human is brought to Equestria in the body of King Sombra, in hopes that he might be able to save the kingdom from the fiends of Tartarus...
A human soul is stuffed into King Sombra's body. Having no idea what's going on, and thinking he is in some kind of coma, he just casually strolls into the Crystal Empire.