Yes, yes, there's a lot of Pokemon. At last count, we have 649 of them—with 19 more announced and probably even more to come as we come closer to Pokemon X & Y's release. You know what that means, right? One lucky Pokemon gets to be number 666 in the national Pokedex. It's inevitable.
But which one?
It could be one of the ones they've announced already. Looking at the options, and assuming they're gonna play up 666 as THE DEVIL'S NUMBER it could be Noivern:
Scatterbug also kind of looks "dark," but I doubt they'd go with something that turns into a moth-like thing. Some over at Reddit are speculating it's probably Litleo, a fire-type that's described as a "hot-blooded Pokemon that is quick to start fight."
"But Patricia," you may be thinking, "that lil tyke doesn't look evil at all! How could he be DREADED POKEMON 666?"
Well, the theory is that this pup will evolve into a Manticore—which is significantly more devilish. According to Wikipedia, a Manticore "devours its prey whole and leaves no clothes, bones, or possessions of the prey behind." That, and—notice the tail? Manticores, in some renditions at least, have the tail of a scorpion. Just like Litleo.
It wouldn't be the first time that something cute turned evil-looking by the end of its evolution chain, either.
Game Freak could always do the complete opposite and give us a peppy, happy-go-lucky lookin' Pokemon just to screw with people. Out of the new ones announced so far, it seems like Flabébé could fit the bill:
I'd be down with that sort of thing, it would be funny. Hell, it could be a Pokemon that's not announced yet. It could be that they don't do anything with it at all—which is the most likely scenario. Still, I'm hoping they'll do something cool with it, whatever number 666 ends up being...but then again, this is Pokemon 420: