A lot of news came out of the Nintendo Direct about the New Super Smash Bros for Wii U a few days ago. One of the biggest news was that Mewtwo will be making a return as a DLC character. This DLC is available Spring 2015 if you buy both the 3DS and Wii U versions of Super Smash Bros.
Also if you buy both versions of the game you will also get the two disc soundtrack of Super Smash Bros. All you have to do is register both games on Club Nintendo by January 13th, 2015 to receive the soundtrack.
Super Smash Bros. for the Wii U is set to release on November 21st and Mewtwo is Scheduled to Release in Spring 2015