That be Yoshi's canine companion, though there are possibilities like Shy Guy and Kamek (depending on what series they'd be listed under in Smash Bros.). May a time hopefully come where all playable franchises from the Original Smash Bros. have more then one playable rep (currently only Yoshi and F Zero are still yet to), and may there hopefully at some point be an Assist Trophy of a character from Yoshi's own games appearing in the Smash Bros. franchise at some point.