This guy in Southern California is without a doubt the master of Metal Dubbing. He takes an existing video (there are several posted below... such as Justin Beiber and Katy Perry and then puts in his own soundtrack that he creates (including all voice and instrumentation.) Brilliant! My favorite is the Christmas twist below, where he takes a death metal video by Gorgoroth and gives it a cheery Christmas tune soundtrack.
So check them out. I've posted his versions followed each by the original.