I meant rival Sonic as a franchise, not as a character. Shadow was still made by Sega, with the same basic gameplay mechanics, so he doesn't count.
As for Freedom Planet, I guess that's something, but even though I haven't played it, it still looks like it was heavily inspired by Sonic. I want to see some completely different gameplay mechanics.
I know, but your criteria was generic enough that I wanted to say Shadow in jest.
Aside from that I'm not too sure what you're expecting with a rival to sonic with the same fast-running as him, but completely different mechanics as criteria. You want a fast character in what sense? With what you mentioned, it can't really "rival" Sonic if it completely strays from its concept and retains its fast running.
In any case, I don't want to leave with the impression Freedom Planet is merely a Sonic clone. Its also heavily influenced by the amazing Gunstar Heroes, and other games, but still does its own thing. It also has a pretty decent emphasis on combat. I'd personally recommend it