"I wish Karyn was here." Jon didn't want to make any wishes without her, since she wouldn't notice what was different.
The stone glowed and suddenly, Karyn appeared in the room, fortunately fully dressed.
But his wish wasn't just granted to him. It was granted to everyone who fit the description of an "average student". So now, there was a version of Karyn standing next to every one of those people. That's a lot of Karyns.