https://www.gamespot.com/articles/e3-2018-super-smash-bros-ultimates-gamecube-contro/1100-6459823/

Super Smash Bros. Ultimate arrives on Nintendo Switch this December, and while it'll support several different controller options, the only way to play the game for many Smash fans is with a GameCube controller. At E3 2018, Nintendo confirmed existing GameCube controllers will be compatible with the game via an adapter, but if you don't have any or are interested in adding more to your collection, you can now pre-order one.

The Smash-branded GameCube controller is available to pre-order from both GameStop and Amazon. It retails for $30; however, if you purchase it from the former, be advised that it appears orders are limited to only two controllers.