This Gamecube Controller Adapter is amazing. It's not like the official version, wich only support Smash, but a sort of "illegal/weird" version of it. It works on every game on the Wii U, Smash, Mario Kart 8, Super Mario 3D World and many other games that are good with a Gamecube controller. And I can use it on the Wii emulator of the Wii U too.
The adapter connects to the Wiimote and make the console think that I connected a Wii U Gamepad Pro, while in reality it's a Gamecube one. "Pratique" like we say in France, since now I can play Project M and Smash 4 on my Wii U easily without having the deal of waiting a thousand years before Nintendo makes new Gamecube controller.
The only disavantage is you can only have one controller on it. At least I can play with it on a butt lot of games now.
That's nice.