https://www.polygon.com/e3/2018/6/13/17461320/mario-tennis-aces-dlc-blooper-koopa-troopa

Mario Tennis Aces will get two additional playable characters after launch: Koopa Troopa and Blooper. Nintendo announced today that the characters will be added to the game as free, downloadable content this summer.

But there’s a bit of a twist to how Nintendo is rolling out Koopa Troopa and Blooper: Players will only be able to get access to those characters early if they take part in online tournaments for Mario Tennis Aces.