A SACRED FIRE ENTEI!
I'm too lazy to browse all the Bank-only Pokémon on Serebii's Pokédex, especially since he hasn't updated many of them with level-up moves, but holy shit this is the best Christmas gift ever! It'd be amazing if Entei actually became usable now, especially since Flare Blitz didn't do THAT much for its cause. Sure, it was better than Fire Blast or Fire Fang, but Sacred Fire... DAMN. I was pretty sure it was going to stay a Ho-Oh-only thing for all eternity.
On the other hand, it's been confirmed that Gamefreak didn't hide the Fairy type on purpose on the Global Link for previous legendaries in order to not spoil a potential retcon. So much for that. Now we have a pixie trio that's not even Fairy-type. Crying shame, because they might've been worth using otherwise. Um, they get Dazzling Gleam? ...I guess?
Edit: The Magma Storm nerf (I guess the proper word would be rebalancing, what with the chip damage buff) that I mentioned a while ago is officially confirmed, however one thing we didn't know about was Techno Blast being buffed to 120 power. Will using the drives have a point now? Of course not, using the appropriate type-boosting item along with Thunderbolt, Ice Beam or Flamethrower isn't that much worse, and these items suck compared to the almighty Choice Scarf, as well as things like the Life Orb or Expert Belt.
In addition, Hold Back was officially confirmed as a complete clone of False Swipe. So... why not give Celebi False Swipe instead of wasting game code? I don't get it. Some people say that was common knowledge, but I call BS on that, because the only reason we even knew about it before the event announcement was because of random Metronome sightings that I can count on a single hand. Good luck extrapolating anything at all off of that.
Edit 2: A suggestion for everyone: if there's no rush for you to transfer your Pokémon, you might want to wait a few days before getting Pokémon Bank. I hear it's nearly impossible to get anything done because of the massive server load, and it's safe to assume the same will happen during the international release.