I don't mash by just pressing B with my thumb over and over. I actually learned how to mash accidentally because of how much fun I have rapidly choosing a character on the CSS while waiting for the stream to be ready with our names and whatnot. I put the middle joint of my thumb on the B button and I slide it back and forth from B to A. I don't know if this is easier for most people, but for me it's easier for me to slide my finger back forth than it is for my to lift my thumb up and press down over and over. The only risk here is just making sure you don't get ahead of yourself and press A first back accident, because if you do then you'll input a dair then you'll buffer the cyclone and you'll just fall to your death.