So, I had this thought, that I don't know if anyone has mentioned. If you click on the 2 question marks in tennis at the beginning, you can play against yourself, and have you controlling each miis, so you can guarantee a perfect game. Respond to me if anyone has mentioned this before. Thanks!

The rules specify that you “must play against CPU in Tennis, Baseball, and Boxing” and win depending on the category. I believe this is applicable to all categories

I had just seen that. Thank you for the clarification.

can I click just one "?"

You would be partially playing against yourself which is not allowed. As stated in the rules for all sports you must play against the CPU and win. This also applies to other categories where you play Tennis.