*sigh*
Ok first of I think this intro is quite well made. The music is good, the animation is decent, everything looks good.
However, having said all that, I really have to question your premise. You've chosen to throw together Sonic, Mario, and DragonBall Z, ok. Except you've also got Mecha Sonic as your main villain. Does it really seem right to have Goku and Vegeta in there when all they're facing is Mecha Sonic? I mean just how powerful can Mecha Sonic possibly be? It could just be me, but I just think that even with the Chaos Emeralds, Goku and Vegeta could brush him aside with little difficulty after having faced the likes of Cell and Buu. It could be for this very reason that Alvin Earthworm doesn't actually include the Dragon Ball characters in his crossover series, but instead just uses the DBZ storytelling style. I don't know, I'm just speculating on that last one.
Anyway, the point of getting at is your heroes and villains need to be appropriately scaled, like you wouldn't pit Goku against Gargamel from the Smurfs; and I just don't think Mecha Sonic is powerful enough to be a threat to Goku and Vegeta. Feel free to prove me wrong though.