The previously announced Nintendo GameCube controller adapter for Wii U will be more limited than fans first believed. Originally the adapter was said to be compatible with all Wii U titles that allowed for the use of the Pro or classic controllers. However, Nintendo confirmed that the adapter will ONLY be compatible with Super Smash Bros. for Wii U.
The adapter retails for $19.99 and allows up to four GameCube controllers to be used. If your heart is not set on using the GameCube controller to smash your friends than you may want to pass up on this limited accessory.