We haven’t seen reports of people having problems with this yet, but apparently in order to claim your Mewtwo DLC, you’ll need to have both your Nintendo 3DS and Wii U linked to your Club Nintendo prior to downloading them on either system, or you’ll need to link them within five days of downloading or you’re not eligible for the promotion. One person who forgot to do this emailed Nintendo support for their response to the issue and this was the reply they received:
I am sorry to hear that you are experiencing an issue with registering your downloaded Super Smash Bros. for 3DS game.
In order to register a game downloaded from the Nintendo eShop your console needs to have been linked to Club Nintendo either prior or within 5 days of downloading the game. If this is not done then the game will not be valid for the promotion.
Please note that this system does not work retroactively, this means if you have not registered the console with 5 days of the game purchase then you are not able to register the game. We are also unable to manually add any purchases made before linking the console.
Ouch. Those of you who purchased both the Wii U and the 3DS version, have you experienced any problems claiming your Mewtwo DLC? It seems like this is a very specific issue for those that haven’t linked their Club Nintendo accounts with either console yet.
