In what could be the biggest thing to happen in Pokémon games in a while, a new type of evolution is introduced. We had a teaser of this a while back when the new form of Mewtwo was revealed, now it is confirmed that this is mega evolution and other Pokémon can undergo it as well. A caption in this new trailer states 'Mega evolution is only possible during battle!' which suggests it may be temporary. During mega evolution the symbol present on the japanese covers of the game is visible above the Pokémon. This looks like it symbolises DNA and could indicate that mega evolution is the result of DNA alteration.