Very nice.
I could see plenty of DBZ references, which may be outside of the Mario world, but I can't complain that it made the battle more interesting.
If Nega Mario returns, maybe using less flashy moves, but still similarly powerful ones, might be a good idea. Also, I didn't get a good view of the areas in which they were fighting. But overall, a very nice animation.
c
A 8 because I think it was a little unoriginal, and I'm comparing it to the many other good animations.