Mr. Fusion is device taken back to the present from the year 2015 in the movie Back to the Future. It is used to generate electricity from nearly ANY raw material (in the film, eggshells, stale beer, and other assorted trash was used) conceivably by the mysterious process of cold fusion, hence the name.

This device is added to Doc Brown's time machine after his trip to 2015. The prop is actually constructed from a Krups coffee grinder.

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http://us.imdb.com/ for some trivial information