The 751st Pokemon has just been revealed and it's the first of its kind. Volcanion is a legendary Pokemon and the only dual fire-and-water-type in the series. It's also going to be the last Pokemon to debut for this generation of the games and you can see it in action in the debut trailer below.
Volcanion will star in next year's Pokemon X, Y, & Z movies and was first revealed in the latest issue of CoroCoro Magazine.
It has not yet been announced when or how you'll be able acquire the Pokemon but you can import it into Pokemon X/Y/Omega Ruby/Alpha Sapphire.