Well, this is unexpected. A brand new Pokémon has been revealed via Japanese magazine Coro Coro.
Its name is Magiana and it is classified as "man-made" (because creating Pokémon artificially worked out so well with Mewtwo). It's the first new Pokémon not to be included in the data within the latest generation of games - X and Y, plus Omega Ruby and Alpha Sapphire.
Magiana is set to be properly revealed in the next Pokémon film, which will also feature mythical Pokémon Volcanion.
Volcanion is the last Pokémon in the current generation. There's no way to officially obtain him yet, but his data is included within the above games for when The Pokémon Company chooses to officially make him available.
This is the way unlockable Pokémon have always been released - they are "hidden" within the game's code until a giveaway event makes them available.
So, back to Magiana. It is not included in the data of any game, which traditionally means it will be included in a future generation of Pokémon introduced by a new set of games altogether.
Second generation Pokémon such as Togepi and Ho-Oh were introduced while the previous generation of games was still ongoing - Yellow had yet to be released, long before Gold and Silver gave players a chance to own these species for themselves.
There may still be another title to launch this generation, then - a Pokémon Z to accompany X and Y.
Or it may be time to introduce a whole new set of Pokémon via the start of Generation 7 this year - which would be fitting, alongside Pokémon's 20th anniversary and the launch of Nintendo's new NX console.