Right before the Elements struck, the Nightmare unleashed a spell out of desperation. A substitution spell. Otherwise known as the correct use of Kawarimi.
Mark Wells only bought an old mirror, so why did he now have hooves, wings and green fur? And where was he? Maybe this great and powerful princess could tell him?
Equestria has a destiny in mind for everypony. A transdimensional guest, however, is surprised to find that this even applies to him, especially since it seems this strange world wants to keep him as its newest infant princess.