Nintendo announced during their E3 Nintendo Direct (http://www NULL.ustream NULL.tv/NintendoUK) this morning that a new Pokémon type was going to be introduced in X and Y.
Nintendo tantalized fans a few months ago with a new Eevee evolution, Slyveon, leading to much speculation about what type it would be. Nintendo squelched all rumors this morning, when they announced that Slyveon is a fairy-type. In addition to Slyveon, some older Pokémon are being reclassed to the fairy type, including Jigglypuff, Gardevoir, and, Marill. The new type is super effective against dragons, which should be nice in some tougher battles.
Pokémon X and Y releases on the Nintendo 3DS worldwide in October 2013.