Mewtwo will be available as a downloadable character for Super Smash Bros. on Wii U and Nintendo 3DS on April 28th. He will cost $3.99 on each platform individually, or $4.99 for both platforms together.
In addition, Nintendo have also announced that Lucas from the Mother series will be added to the game as a downloadable character in June.
Nintendo say they will also open a poll on the Super Smash Bros. website later today, where fans will get to vote on additional DLC fighters, and these votes will be taken into consideration during the development of future DLC.
Update: Mewtwo and Lucas trailers added.