March 31 is the deadline for player's chance to download Mewtwo as a playable character in Super Smash Bros. for the 3DS and Wii-U. Mewtwo will become the first downloadable fighter in the Super Smash Bros. franchise, Nintendo's mascot fighting game. In order to obtain the character, players must join Club Nintendo and register copies of both the 3DS and Wii-U versions of the game. Despite the deadline of the end of the month, the actual character will not be available until a later, still unspecified date sometime this spring.

There are currently no plans for further downloadable characters; though it is entirely within the realm of possibility, Club Nintendo's discontinuation makes it an unlikely possibility. Blue vixen fans will just have to wait (and hope) for the next console.

Update (April 1): Mewtwo will be available April 28, and further downloadable characters have been verified (though, once again, not Krystal). [Sonious]
Update 2 (April 2): There is now a system in place for voting on characters; I forgot who I picked. It is available until October, so don't expect a quick turnaround. Also, the March 31 deadline was only for a free Mewtwo; Mewtwo will be available for $3.99 for one game or $4.99 in bulk.