Hate to say this but, it isn't really original!
Yes we shouldn't be comparing it with SMBZ, but you did take concept from it! The fighting style, effects and humors:/
Well if you are going to be making a full flash movie Cast of Shadow. Don't give up!
You need to make the storyline really good and griping if you want a Win!
The music in the fight round 2 didn't really fit the battle, it surely fits SMBZ :) (no offense).
Mario seemed to be stronger than Luigi, Luigi seems to fight too stupid. Please make them equal. But I did like the part Luigi was throwing punches at Mario before entering the first tunnel.
Fight style you borrowed from SMBZ, Mario performing the "blow to the gut", "multiple punches" etc. But at least you didn't make it seem like SMBZ/DBZ (fighting in the air). But if you want this to be that original, don't make them fight like SMBZ: fighting really fast:/
The humour you used, Luigi upper cutting Mario, and the music breaks...that doesn't even fit the situation.
But anyway...I'll be looking forward to the full episode. Surprised you managed to create a flash that the quality looks so much lie SMBZ:O
Just come up with more innovative fight choreography and original battle. Show off different background rather than the ones in SMBZ.
Music used in this battle was good, I like the intro battle music:) But don't use music from SMBZ.
Reduce the humor jokes, unless they would really make us laugh!