Anyone from any time, which means baddies we've already busted could pop up too.

[Baddies, potentially lost. Y'know. People. That aren't baddies. Sonic's going to refrain from bringing that up, he's sure Shadow can connect the dots himself anyway.]

I can think of more than a few that I'd rather not have to tangle with again. The question is, how could we even prepare for a possibility like that?