Edit: Oblivion Wing is said to be an 80 power, 100 accuracy attack that drains HP. However, there are conflicting reports on the magnitude of the draining, some say 50%, some say 75%, some say 100%. I assume that as a cover legendary's signature move, it's going to be MUCH better than a Giga Drain with 5 more power, so I think it'll be more akin to a Draining Kiss with 20 more power instead. As for Pokémon-Amie, its happiness factor is separate from the one that already existed, so Sylveon's "traditional" happiness won't be topped after evolution. Also, judging from older information we have, Moonblast's added effect is lowering special attack (at a 10% rate like its counterparts, most likely).
Edit 2: Remember that Minotauros leak from the pre-BW1 period? Well, Minotauros still isn't a thing, but something else from the same leak is: moves that affect the terrain and create a variety of effects. Sylveon has such a move, called Misty Terrain, which makes all grounded (ergo, non-flying, non-levitating) Pokémon immune to status, AND they also take half damage from Dragon moves. Problem is, that last part is NOT in the move's description... but rather explained in one of those signs on the side of the road. Yikes. Quite frankly, I'm not sure this'll make much of an impact, because it appears both sides are affected, so YOU won't be able to status your opponents and nail them with the full power of your Dragon moves, either.
There's also another one called Electric Terrain, which was found on Magneton, though the effects are as unclear as you can get for now, so I won't go any further for now. In unrelated move news, Crafty Shield was spotted on Klefki, and it's like Protect, except it defends against NON-attack moves. Finally, Phantom Force is a Ghost-type Dig. So physical Ghost FINALLY gets something stronger than 70 attack... AND IT'S A FUCKING DIG CLONE. Goddammit Trollfreak.
Edit 3: Fairy isn't weak against Fighting. Fairy isn't strong against Ice. Now we can add to the list: Oblivion Wing isn't even a Dark move! That's right, they weren't content giving us lies with that one episode of Pokémon Smash, but the July issue of CoroCoro gave us false info too! Man, Yveltal could've been so awesome with a Dark Aura-boosted Dark draining move. It's like they didn't want anything defeating their precious Mega Mewtwo.
Edit 4: Remember when I said making popularity a factor for who gets to megavolve was a bad idea, because many Pokémon are popular because they're so powerful? I'm sure as hell not changing my mind after this. No one found the Mega Stone yet, but just the fact that there's a Super Training balloon of what looks a lot like a Mega Tyranitar is absolutely scary. I'm just praying, if that's a thing, that it gets an ability that makes megavolving a poisoned gift just by losing its current ability, like Venusaur.