A seven hour special Pokémon stream was shown in Japan today and right at the end a surprise reveal was made in the form of Mega Rayquaza for Pokémon Omega Ruby and Pokémon Alpha Sapphire. The Mega was revealed by the official Pokémon YouTube channel for outside of Japan straight afterwards and you can see a trailer for the Pokémon below:Mega Rayquaza can learn a special Flying type move known as Dragon Ascent which is said to be extremely powerful. Mega Rayquaza also has a new ability known as Delta Stream which means all other weather abilities and moves will not work as long as the Pokémon remains in battle. It's worth noting that the ability also makes it so moves that Flying type Pokémon are normally weak to will only deal normal damage to any Flying type in battle. Mega Rayquaza also gets a boost in all its stats and remains a Dragon and Flying type Pokémon.
Official artwork for the Pokémon has yet to be revealed but we'll no doubt get some when CoroCoro leaks.