This month's edition of Japanese magazine CoroCoro has just started to leak and brought with it the reveal of three new Mega Pokémon for Pokémon Omega Ruby and Pokémon Alpha Sapphire.
The magazine has revealed a Mega form for Sceptile which changes its typing to Grass and Dragon and gives it the Lightning Rod ability. Mega Swampert keeps its typing and gains the Swift Swim ability. It can also learn Hammer Arm. A Mega form for Diancie has also been revealed. It keeps its original typing but little else is known about it currently.
The new artwork for Kyogre and Groudon, which previously suggested that the two may have Mega forms, has now been confirmed to indeed be either new forms or Mega Evolutions. The translations are a little rough (it's currently not clear just which translation is the correct translation) but it seems the new forms/Mega forms of Kyogre and Groudon are known as Primal/Prehistoric/Primeval Groudon, and Primal/Prehistoric/Primeval Kyogre.
The magazine also shows off the new designs for May and Brendan, as well as showing off Steven Stone and seeming to confirm that he has a Mega Charizard X. It also shows off Team Aqua and Team Magma and confirms that the team you face will depend on which version of the game you play.
The leaks also confirms that like in the original Pokémon Ruby and Pokémon Sapphire you have the choice between the Mach Bike, which moves very quickly, and the Acro Bike, which allows you to perform tricks. Apparently the item to activate Mega Evolutions this time around is a "Mega Bangle" rather than the Mega Ring seen in Pokémon X and Pokémon Y.