Ever since the announcement that extra characters will be available through the scanning of QR codes, fans have been speculating on who those characters could be. Thanks to the recent update to the Japanese Mario Tennis Open website, fans can rest assured that a total of seven characters will be unlockable through QR codes. However, Blue Yoshi has been confirmed to be one of the QR code unlockables, leading many to believe that the rest of the characters may also be simple color or costume swaps with existing characters. According to the website, there will be a total of seven QR characters.
In addition, the Japansese website updated their characters page, officially revealing the full roster. Baby Mario, Baby Peach, Luma, and Dry Bowser are indeed the final unlockable characters.