Harry was having a good day at the Place that he lived. Yes sir. Nothing was wrong. He had started to grow facial hair, Ron's voice had changed, and Dudley had been diagnosed with prostate cancer. He would soon be back at Hogwarts endangering students' lives and generally being a disobedient twerp.
Meanwhile in the future and by that I mean the present, Marty Mcfly was in his time machine.
"Hey, I fixed it!" He said
"Great!" Said the Doc "But a page of your Harry Potter book is caught in the Flux Capacitor"
"What!" Said Marty, but it was too late, he went back to the present. Or to the Harry Potter. Something like that.
Harry Potter was jamming with Ron. Then a time machine car smashed their jam box.
"Not cool." Said Ron, his voice changing octaves at least four times
"Oh, no." Harry moaned as Marty was confused
"Where am I?" He said as he was confused
"More Important is when." Said a voice from behind a bush
"Sonic the Hedgehog!" Said three voices in unison
"Yes!" Cried the Sonic the Hedgehog "Time for some serious speed."
"Not Today!" Said a voice
"Oh, No!" Harry said "It's Voldemort."
"And Biff" Said Marty
"And who ever is currently my enemy!" Said Sonic the Hedgehog
Harry and Ron went for their wands, but Biff whipped out a copy of how every fight in Harry Potter Book ends.
"Oh, No!" Every one said "It's a paradox!"
And their heads exploded. And Dudley did a butt dance. With Marty's girlfriend. And it was good.