Like always, Donkey Kong showed up for the Mario spinoff game. For the Generation Z kids, Mario's first game was Donkey Kong, thus why they don't feel odd including him.
Like Bowser and Wario, Donkey Kong is in the powerful class in tennis.
He's quite a good character to play with. I oddly didn't find many players that were that good with Donkey Kong however.
He was in the top ten of my picks, but I certainly favored Bowser, Chain Chomp, Rosalina, and Wario though.