First off is at the VERY beginning, before it shows the first character, there is some horrible lag with the snow and the scrolling floor (do you trace bitmap any of your backgrounds or floors? If so, that is a big NO in sprite animation because of how much lag it can cause). The music was fine until the fight started, at that point it got rather boring and unfitting for a fight. The fight really didn't have much flow to it and didn't really seem to have the feeling of an impact for each hit. Some movements went by far too quickly so have to determine what's actually usable and what the viewer will be able to see and comprehend.

The animation was alright and there were little issues with it as a whole. However this ( http://prntscr.com/4cf03j ) is an issue with the camera and it also made us, the viewers, able to see what we shouldn't see. I'm not sure what happened so I can't say how to fix it. Another issue was when Mighty and Ray were running and trees were going past them; and, it lagged to high hell. I'm guessing you used the blur feature in Flash? It's a bad idea to do so. If you want something blurred (like background or foreground things) try using something like Paint.NET or Photoshop to blur an actual image to avoid this issue. Some hit sparks, dust effects and a better wind effect would have been nice, but that's just my preference.
I understand what you were trying to do with the song and it fit with the video; but, it just wasn't for me so I won't comment much on it.
If you have anymore questions shoot me a private message. I'm always happy to help and hope you find my comment useful in some way! Have a good day.

None of the buttons work, except for "Scenes" and "Main Menu", I had to right click and hit play to even view the animation. Some of the animation was either too slow or didn't show any fluidity, while the camera was also too zoomed in to the characters while he was attacking. FLOATING LETTER, you could've found some poses to work around that like he actually went to the letter. Sonics' dash off the steps was unnecessary, a jump would've worked better. Saw the boundaries for the black box fading in, and for one of the skies. Multitude of sound clips for characters playing out of nowhere and unfitting music playing for the scenes and the sudden end.
I know you lost the .fla, but uploading something like this (especially with it barely functioning) is not good. If you lost the .fla then begin remaking it, you're not obligated to upload this.
Overall, I wouldn't give this a good rating but some of this animation is not that bad if you'll continue! If you need someone to preview, test and help you with the flash I'm open to help! If you have skype, my contact is on my Newgrounds or message me on Newgrounds.