COROCORO INFO, COMIN' ON UP!
First off- Mega Altaria! Mega Altaria gains the Dragon/Fairy typing, as well as the ability Pixilate.
And it seems the new megas aren't restricted to Hoenn pokemon. Here's Mega Lopunny, who's now Normal/Fighting type with the Scrappy Ability.
It also seems like changing Pikachu's clothes also gives him special clothes. Pikachu Rock Star gets the move Meteor Mash, Pikachu Ph. D. knows Electric Terrain, Pikachu Pop Star knows Draining Kiss, Pikachu Belle knows Icicle Crash and Pikachu Libre knows Flying Press.
And don't worry, Salamence hasn't been left out of the fun. Mega Salamence is confirmed to have the ability aerilate.
There's a Contest Idol called Lucia who gives you special clothes for participating in Pokemon Contests.
And finally, SHINY MEGA METAGROSS. It appears you can get a shiny Beldum from an event, and the Beldum will be holding it's mega stone.
Some thoughts of my own? From top to bottom:
It's so fwuffy!; ...I have no words; Pikachu with Flying Press? Okay.; Salamence get's Talonflame's priority ability? Joy.; Yay, Clothes!; and there goes the value of my Shiny Metagross...But DANG, it looks epic.
(all information credit from Serebii.)
EDIT:Oh, it looks like there's an ounce more of information, mainly about contests.
Apparently, Feebas's evolution is gonna be contest-based again. Also, pokemon can mega evolve in contests, which boosts the Exite Meter and Appeal, but can only be perfrmed when the Exiteme Meter is filled.