The yoshis, shy guy, boo, and chain chomp are available through coop challenges. The rest are available through entering tournaments and claiming the following month
Yeah, Mario Tennis Aces. A game that has an incredible roster since Mario Kart Wii, Mario Super Sluggers, and even Mario Golf World Tour. Love it. I sure hope that they make Mario Golf, Mario Baseball, Mario Strikers, and even Mario Sports Mix for Switch, especially a roster as great or even better.
It's very strange why they didn't give out alternate colors / palette swaps to these characters. That would have added a little more variety on the scene.
I see the alternation of - Mario (special Racket) - Mario and Wario Bros. (classic suits) - Bowser (dressed) - Toad (tennis dress and the second hat) - Toadette (tennis suit) - Chain Chomp (three variations with the hat) - Blue, Cyan, Orange, Pink, Purple, Red and Yellow Yoshis - Blue shelled Paratroopa - Boo (many variations with the hat) - Blue- and Red-shelled Koopa Troopas - Blue, Green, Cyan, Yellow, Pink, - Spike (three variations with the bands)