(Same story as New girl, thought things might get more interesting if Jon hadn't removed the stone from the equation)
In the bathroom, Jon stared at his reflection in the mirror. Am I really going to do this, he thought to himself. He had a pretty good idea how to make it temporary, but even if it was temporary it was still a big change to consider. Still, Stacy had seemed really bored all night. The first bit of excitement he'd seen in her was when she'd opened the Selena Gomez CD and asked him to listen to it with her. No matter how much he wanted to make Stacy happy, though, he really had no interest in listening to the CD. Maybe if he was a 13 year old girl himself he'd have more interest.
"I wish that any further wishes I make while in this bathroom tonight would remain in effect until I say the phrase 'I'm really Jon Merlin' at which point everything would become as it is now but that Stacy will subconsciously remember any fun we've had together," Jon said to his reflection. He blinked as the stone flashed to signal the granting of his wish.
Figuring he was now safe to make his real wishes, Jon took one last deep breath before going on. "I wish that when I step out of this bathroom I will become a 13 year old girl named Mallory Evans, a school friend of Stacy's whose parents had to be away overnight unexpectedly so Aunt Lisa and Uncle Rick agreed to let her stay with them. Also, I wish that my clothing and physical appearance as Mallory will be based on the qualities of girls that Stacy is friends with and wishes she was friends with. I wish that while I am Mallory I will think and act like a 13 year old girl. I wish that Mallory's personality and interests will be based 40% on Stacy's own personality, 30% on the personalities and interests of Stacy's 3 closest friends, 20% on the most popular girl in Stacy's class, and 10% based on how everyone in this house other than Stacy and I think a 13 year old girl should act. I wish I will think of myself only as Mallory Evans when I step outside of the bathroom but that I will still remember being Jon Merlin, too. I wish that for as long as I'm Mallory I will have her memories as well as my own. Also, I wish that as long as I'm Mallory my educational knowledge will be limited to that appropriate for a reasonably popular 13 year old girl who gets average to good grades."
With that done, Jon opened the bathroom door and walked out of the bathroom.