Well I haven't seen you around for a while. So this is a Sonic the Hedghog fanfiction? We'll see how this goes then.
So this is a prologue. It leaves out some information, referring to characters, and we already have our antagonist! At least it gives a few questions as to why Mephiles is beating the crap out of Shadow. However, leaving Shadow to die seems a bit off. Personally, I'd be sure he was dead. I know it'll be hard to actually put in a way so that Mephiles would allow him to live, but it just doesn't make sense. It could be interesting if you geared it to be a plot factor, since Shadow already survived once before.
I would also like to know why Shadow couldn't fight back. But I guess you can answer that in future installments.
Just be sure to look over your work, especially for things like spelling and grammar. I'd suggest typing it up in a word processor, or at least spellcheck it.
That aside, it looks promising. Good luck on your writing!