This thread talks about different fan-made versions of Super Mario Bros. 1.
My favorite version of it would have to be the one based on the Japan-only "Transformers: Convoy no Nazo". The Transformers game is kind of infamous outside of Japan, especially to American retro, '80s Transformers fans. One of them created a hateful song to the game. In Japan, it is either so popular or infamous, it became a Japanese Internet meme along with some other NES games like Action 52, The Cheetahmen 2 (which also has a Genesis/Mega Drive version) and the NES version of Spelunker. It was also ported to the Virtual Console only in Japan, probably because 2chan members sent a lot of requests.
Here is what the Transformers version of SMB1 looks like: