Not bad, but could have had more work.
The concept of your flash is way too over done. The problem is, is that the flash isn't good enough to stand out from all the other character vs character movies out there. The fighting wasn't too bad, and was fairly interesting to watch, but you might want to add some reason why mario and luigi are fighting and impact sounds when they fight are also good too. This also needs some work in the basic presentation of the flash such as the preloader, which was poor. Fix some things, not as many as you think, and you'll be known in no time :)