As it turns out, the 69 figure I put forward yesterday is the one that's accurate, as there's no spot between Yveltal and Zygarde, our third cover legendary. You can learn Beta from it by equipping the Enemy Skill materia... sorry, that was just too easy. The name actually beginning in Z suggests a possible return to the deluxe version formula this gen, though I wouldn't call it just yet. In addition, runners make a return in this game, with Zapdos being found in the middle of nowhere. Oddly enough, it happened to rain when it was found.
So, 69 new Pokémon, plus events. How do I feel about that? I've had time to think it over, and quite frankly... I think this is a good idea, for two reasons. First, and most obvious, they didn't have to run their well of creativity dry, with the only dubious Pokémon being Klefki - I can forgive Doublade considering what it evolves into. This is as opposed to gen 5, where them being forced to make over 150 to make a Pokédex made entirely of new Pokémon gave us more than a few... questionable designs (though we also had some of the best ever, mind you).
On top of that, it's clear that much of the effort went into the mega evolutions, which (at least in theory) are meant to help out weaker Pokémon. I've always said that making less Pokémon, but focusing on making the existing ones better, was the way to go to make a more varied game. And aside from the fact that they gave some to the likes of Blaziken and Garchomp, that's the path they chose to go down, and it would be hypocritical of me to complain. So, thumbs up to Gamefreak for that.
Edit: Deleted due to obsolete information
Edit 2: Zygarde's ability, Aura Break, reverses the effect of Xerneas' and Yveltal's abilities. Whether the word "reverses" means canceling out, or outright causing them to weaken the moves they're supposed to boost, is still unknown. As for its stats, it appears relatively well rounded, except for physical defense which is much higher than the rest. Also, the thing's Dragon/Ground. Gamefreak sez: "We know Dragon is overpowered, but here, have yet another Dragon pseudo-legendary and yet another Dragon cover legendary!"
Speaking of typing, you know how I found it weird that Goodra is mono-Dragon? Well, Florges is mono-Fairy. Are you serious? The thing is bound to a flower, it evolves TWICE, and NEVER gains the Grass type?
Edit 3: Here's the REAL stat spread for Mega Mewtwo Y:
106 HP, 150 Atk, 70 Def, 194 SA, 120 SD, 140 Spd, for a total of 780
For reference purposes, the damage boost obtained through the SA increase is 20%, which is less than the Life Orb, BUT you don't have to deal with recoil, and you have extra special defense and speed. Shame about the defense drop, but fortunately for it ubers tend to revolve around special moves anyway.
Edit 4: Nothing new on the leak front, but I just wanted to share the fact that one of my regulars, who's trying to stay spoiler-free, basically ran into a picture of all the new Pokémon... on a pr0n site. THIS IS WHY YOU DON'T INTRODUCE EXACTLY 69 NEW POKÉMON IN A GENERATION, GAMEFREAK.
Edit 5: Here's the most recent Kalos Dex update I could find (missing Audino, confirmed at #123 Central), as well as the newest portion of the National Dex.
Edit 6: Togekiss is now Fairy/Flying, as expected. This swaps a few weaknesses and resistances around, but the especially good news is that it now gets a much better secondary STAB type, and as a result could be a mainstay of the metagame once again should the Fairy type not be particularly stacked - and maybe even if it is.