I don't think you can get away with Mega Mushrooms on the ATP or WTA tours.
http://www.nintendoworldreport.com/video/40505/mario-tennis-ultra-smash-footage
Mario Tennis: Ultra Smash is one of the new Wii U games revealed yesterday that's coming out this year, and we've got some footage for you.
Here, you see what happens when Giga Bowser tries to swing a tennis racket:
Then we have a full set from the show floor, in which Mega Mario gets his revenge: