There's two versions of Super Smash Bros. 4 coming, one on Wii U and the other on Nintendo's handheld, 3DS. The content is the same in both versions, but the portable game presents a cel-shaded visual finish with black outlines (to better define the characters on the small screen) and the Wii U version offers detailed HD graphics. At the moment Super Smash Bros. 4 has 11 confirmed characters: the two aforementioned additions, as well as Mario, Donkey Kong, Link, Samus, Kirby, Fox, Pikachu, Bowser and Pit.
Update - A twelfth character, the Wii Fit fitness trainer, has also been announced.
3DS
Wii U