For those who get the error code "104-2210" in Splatoon. https://github.com/PretendoNetwork/Nimble/releases Move the file "30_nimble.rpx" at this url to this SD card directory. :\wiiu\enviroment\aroma\setup\ There is more in the reply
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Open Settings and delete the Splatoon shared save data. Setting/Data Manegement/Organize Data/Organize Body Storage Memory/Splatoon/Shared Save Data/Erase This should solve the problem. I'm using the Japanese version of the Wii U, so I may have the notation a little wrong.