You need to ask for the receipt everytime your go and purchase things, not every store gives them out even though it's their obligation...
To redeem the code you need to have a Club Nintendo account and register your Wii U. You need to associate the Club Nintendo account to the Wii U.Once you do that Mario Kart 8 you should redeem your MK8 code, which is located in the game case.
If it didn't come with the game then... bad luck I guess. You can call customer support and ask for help though.
"I've Underestimated the Horse Power from Mario Kart 8, I'll Never Doubt the WiiU's Engine Again"







