Reshiram, Zekrom and Milotic have been confirmed to make an appearance in the upcoming Super Smash Bros for the Nintendo 3DS. Masahiro Sakurai (桜井政博), Director of the games, posted on Miiverse that a new stage based on N's Castle and the Unova Pokémon League will also be featured in the game.
Source:
https://miiverse.nintendo.net/posts/AYMHAAACAABnUYoA29XTHA