Well done, but it seemed a bit hurried.
This was a very good effort, had good length and music, but the timing and spacing of said time was a bit off. There were moments that felt like fillers like when Mario was ducking the hammers he was down for too long and I almost stopped the movie there.
It was really clever the way Bowser Jr mimicked Mario, I remember thinking Mama Mia!
I really liked the variety of bosses, but one thing that got on my nerves is that some of the sprites did not match in resolution, it looks bad when the pixels aren't the same size. Also, I know it's a hassle, but whenever people use the newer Mario sprites, I know I for one would appreciate it if they opened them up in an editor first, even if it's just paint; and remove all the gray dots around the edges.
Like I said I know it's a pain but the one time I tried to make a sprite movie, my first choice was those sprites and I knew immediately that if I would want to see clean sprites than so would others. So, all I had was paint at the time but I still took the time to clean up an entire sheet of Mario, Luigi, Toad & Bowser. If you have something more advanced than paint though than it should be easy. Some day I will try sprites again.
I know I have nothing to show for it, I've been animating in flash for about 5 years now but I've never finished a project, at least not one I considered worthy of submission. My old computer died a horrid death so over 40 projects were left for dead forever. It was discouraging, but I've since started a few more, I hope to actually finish them!
All in all a decent attempt, it really needed sound effects though as I got bored a few times throughout. If the music wasn't so good and well attuned I may have blammed this, but I scored it a 3 average. I think you did a good job though, I can tell that you at least put a lot of effort into this. Keep on animating, you will get better! As long as you don't get worse, you will have the respect of most of the users for at least having actually submitted something!
Lastly, the basic fonts were somewhat of an eye sore; just look up some Mario fonts or use something other than a basic font; it makes the flash look like an old Powerpoint presentation.
Oh and almost forgot: why didn't Mario finish Bowser off? Or at least drop kick him, there was almost no visible fighting or powerups in the movie. That dropped my rating by 1 point, so it's a 5/10.
Shoot for the moon, and hope it doesn't shoot back!