I'm not sure how I missed this the first time around, but I recently stumbled across a trailer for a Mario fan film that had been created nearly four years ago.  Doing a bit of research led me to this page, in which the animator mentions always wanting to have a film on TMK's Fan Films page.

I don't know if anyone else here at TMK had seen this before, but the animation quality is fairly impressive for a fan film, and it features a remix soundtrack by Mustin; these things combined surely earn it at least a mention here on the blog!  Go take a look at the Koopa Force trailer.

Source: Try4cdCubed's IGN Blog
Youtube: Koopa Force trailer