*At this point, perhaps it's a good idea to recount what effects the magic stone has had on everyone involved in the story to this point.
Jon Smith, our erstwhile protagonist, is now Jenny Smith, a sexy, bimbo-ish cheerleader type. She no longer has any knowledge of the stone.
The four bullies - Biff, Reggie, Jim and Ronald - are now also cheerleaders - Buffy, Regina, Jamie and Roni. They are all friends with fellow cheerleader Jenny. They remember going to see Jenny and Karyn one night, but only to bring thanks (not threats) from Sarah McMillan for helping with her test while she was out sick.
Sarah McMillan is the same as she ever was. The only difference is that she is friends with cheerleader Jenny Smith.
Karyn is physically the same (only with the hair and the breasts she got earlier). She remembers the 4 guys being changed into cheerleaders. Because she was not present when Jon became Jenny, she only remembers Jenny. She also remembers the wishing stone. She and Jenny are still friends, but not quite as close since they have less in common. Jenny told Karyn about the stone because she's Jenny's smartest friend.
The only person in the area who remembers everything as it was is Gary Meadows, Buffy/Biff's father. He also knows about the stone, but after the confrontation with Miriam Smith, he doesn't dare go anywhere near their house to retrieve it.
And the stone itself is somewhere in the Smith household.*
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"Karyn! You look kinda, y'know, weird. You all right?"
"Ugh!" Karyn said, shifting her books. "It's these monsters on my chest! I don't know how you've always stood carrying around breasts this size!"
"Well, like, gosh - I never think anything about it, y'know? They're just, like, out there."
"Yeah, they're out there all right."
"Besides," Jenny said cheerily, oblivious to Karyn's grubling tone, "It's nice that we're the same size - that way we can borrow from each other when we need to."
"For now, I guess. But sooner or later, we have to fix this."
Jenny looked confused. "Huh? Karyn, what're you talking about?"
"The stone, Jenny. We gotta figure out how to get the stone to put me back to normal."
Jenny stopped dead in her tracks, her confusion deepened. "Karyn, you're not, like, making any sense! Your boobs and mine have always been about the same size."
Karyn looked at her in amazement. "Jenny, you didn't make any wished with the stone, did you?"
"What stone?"
"The wishing stone! The one you used to accidentally give me these breasts and this hair!"
Jenny gave her friend an odd look. "Karyn, have you been, like, watching too much of that science fiction stuff again? That 'Star War Treks' or whatever?"
Karyn's head spun - Jenny didn't remember the stone. What had happened to it? And where was it?