Demo versions of X&Y were available to play today at the Pokemon Game Show in Japan, and we've got plenty of images and information. Remember that these are demo versions of the game and may not reflect the final product.
First off, Mega Evolution is triggered by a simple button on the bottom of the battle UI when a Mega Stone is held, as shown here:
It was possible to ride a Skiddo and Rhyhorn in the demo and there was a bit of Pokemon Amie:
Fenniken had the moves Psybeam, Flame Charge, Fire Spin and Tail Whip, which may mean that it does evolve into a Fire/Psychic Pokemon as previously suspected. Helioptile has Tail Whip, Thundershock, Quick Attack & Parabolic Charge. Sylveon has Swift, Quick Attack, Fairy Wind & Tail Whip. Froakie has Water Pulse, Quick Attack, Lick and Round.
The player character runs by default, with the B button being used to walk.
This mysterious footage was also shown near the end, a battle with graphics unlike any expected Pokemon media. More on that as it surfaces.
For those of you who play the TCG, Fairy type will be joining the roster when the X&Y series begin to come out, with the icon being shown in the poster below:

I am also very excited to announce that a trailer for
Pokémon: The Origin was shown at the Game Show.
I'd hate to spoil any potential feeling of awe by explaining what it is, so I think I'll let the video do the talking. You don't have to know Japanese to know what's coming, and I couldn't be more excited. It'll appear in Japan on October 2nd, whether or not it will be shown elsewhere or when it'll be translated is unknown.