We’ve known since Pokémon Omega Ruby and Pokémon Alpha Sapphire were revealed that the titles would introduce mega evolved forms for legendary Pokémon.
The latest mega evolutions revealed are for the legendary Eon Pokémon Latios and Latias. Players can catch Latios in Omega Ruby and Latias in Alpha Sapphire. The mega evolved forms of the Pokémon are more or less identical, but they each gain a new move through the evolution.
Have a look at these moves and other legendary Pokémon you can catch in the games in the new trailer below.