It's good
No seriously it is. I like the animation and the effects for the chars powers
And had we never had SMBZ I would be a major fan.
But it could use improving in the following areas (IMO only),
1) originality, all your characters are the same tired rehash of what we have seen before. That is to say if they have personality. (Cowardly Luigi is getting beyond daft now, yes i realise he is according to nintendo or something but still)
2) The text is flat, adding little bits for Mario and Luigis accents doesn't make you care about the characters one jot.
3) Red bowser? I didn't like metal bowser in SMBZ and this is more of the same vein. It looks...terrible.
4) I realise this may seem stupid to say but why include Silver? Tails is by far the more interesting choice surely? I mean silver is just a pointless addon made yet again by Sonic Team to try and gain more money from the series, best ignored.
5) It lacks the right pace, I am not sure how to describe this but there was no sense of urgency or concern about any characters (see also point 2 on this). I didn't feel like anyone was immediately about to be killed. And surely thats the point of this flash?
Anyway i am getting on and off track. The point is this is basically a clone of SMBZ. It is not done badly but in order to shine out above that series you have to pull ALL the stops out. Because that is always what this series will be compared to.
Keep trying and practicing, you can likely do really well. Maybe try to work on a more original idea. Hard thing as most ideas are there already but it's not impossible.