A Back to the Future Part II fan theory suggests that Doc Brown could've been up to something other than he originally implies in the film.

A few years ago, a fan theory made its way around the internet that I absolutely love: The Goonies and Back To The Future ...

Instead of skating, though, he was hovering: a real-world Marty McFly, the time-traveling teen who glided on air around Hill Valley in Back to the Future Part II. The Hendo hoverboard ...