A thumbs up
It was well done. Not much needs to be said about it really. It's a sprites-only collab about Sonic characters (plus multiple cameos) duking it out in fast-paced action. It's quite apparent that all the members here were inspired by the Super Mario Bros. Z series, but since that's the face of good sprite animation, there's nothing wrong with that.
I'm sure you've heard this multiple times, but this collab isn't really "oozing" originality. We have the same Sonic sprites in every part, save for just one. The very same Sonic sprites used in SMBZ. The sound effects are rips from SMBZ (which were originally ripped from Dragon Ball Z, but I don't care about that sort of thing). And the style of fighting is, what do you know, based off Super Mario Bros. Z.
It's nice that you gave us a warning before watching the movie that it contains generic fighting, but that doesn't excuse this collab for what it is. But if you can get past all the negatives of this flash, what we still have here is some pretty solid animating skill. At least nobody stood out as awful. Everybody knew what they were doing, knew what they were getting into, and pulled it off. The result, was watchable, maybe a GOOD time waster.
The minigame wasn't anything special. Just attack until you can pull off a powerful Special move, and start using your MP to heal once you're at low health. It didn't take much skill to beat (at least not for the default difficulty). I couldn't figure out how to switch characters though. I was stuck with Mario. My only problem with the minigame was it's lack of appealing interface. A life bar instead of just numbers standing out in the open would have been ideal.
Overall? Well, like I said, a pretty solid collaboration. It included a scene selection, and bios and the whole deal. But did the intro really have to be so long? A simple "skip" button would not have been hard to make.