The sprites are really good, but it seems to be a beta because i couldn't find any specials or supers, only normals.
Noctis's version is still the best Natsu we have.
Umm....i think he is not based on this animation, Mr. 4x3l made more characters in this DBZ Extreme Butouden style, even Ben 10 and El Chavo got this treatment.
This stage has nothing to do with JoJo as far i know, it's just a original stage. It guess it's a coincidence that it resembles that stage, since i saw this in a JoJo compilation.
I'm quite sure there's a mugen version of Ronaldinho Gaúcho (Brazilian ex-soccer player) on Mugen Archive, if someone could upload it there, I would be very grateful.
If this character doesn't exist, sorry