Nintendo was always going to go big with the release of Mario Kart 8, but with the new Bonus Game Promotion they've pinned their colours to the mast - if you buy Mario Kart 8 at retail or via eShop and register it with Club Nintendo, you can get one of 10 games as a free download. This is quite special.
Those games are: Nintendo Land, New Super Mario Bros. U, Monster Hunter 3 Ultimate (Wii U version), Game & Wario, Pikmin 3, The Wonderful 101, The Legend of Zelda: The Wind Waker HD, Sonic Lost World (Wii U version), Mario & Sonic at the Sochi 2014 Olympic Winter Games and Wii Party U. It's worth noting that most of that list sits among the very best of Wii U's lineup.
Codes must be registered between 30th May 2014 and 31st July 2014, and downlaods will be received by 31st August (although we'd suspect they'll come significantly earlier than that). Finally, remember that this means the Special Edition hardware bundles Nintendo recently announced essentially contain an extra game of your choice - that's quite a deal!