The first DLC fighter in Super Smash Bros. for Wii U and 3DS was Mewtwo.
Mewtwo was a returning character from Super Smash Bros. Melee, where it had originally appeared as an unlockable fighter. It skipped Super Smash Bros. Brawl, making its return in the Wii U and 3DS games especially notable. Nintendo announced Mewtwo as downloadable content in 2014, before the broader DLC lineup was revealed.
Mewtwo became available on April 28, 2015, although players who owned and registered both versions of the game through Club Nintendo received early access on April 15. Its release marked the beginning of the games’ post-launch fighter expansions. Later DLC added Lucas, Roy, Ryu, Cloud, Corrin, and Bayonetta.
Players sometimes confuse Mewtwo with Ryu, Lucas, or Roy because all three followed soon afterward in the DLC rollout. Mewtwo was nevertheless first, and it was the first downloadable fighter for this Smash installment—not the first DLC character in the entire franchise.