Hey... it's pretty simple...
First of all... i'm loading the game via Loadiine with Loadiine GX2 MOD.
I assume you already have the EUR mario kart version... so...
1. Download the DLC from a reliable source (inside the DLC folder should have more than 4 folders... the one i've downloaded first had only 4, the one that did'nt work)
2. Download Loadiine GX2 MOD if you yet don't have it (search for Loadiine with no legit DLC support)
3. Update the game if you haven't yet (as far as i know, the latest version avaliable is v64 (shows 4.1 on the game) OBS: merge the update files with game files (overwriting it when asked). Using folder update and "update mode" on loadiine is known to have bugs) I've download the update from NUS grabber, but it gave me 0005000E1010ED00 folder with more than 78 files. So what now?
4. Put the DLC folder in the game folder (after you do it... you'll have the DLC (the name of the DLC folder should be aoc0005000c1010ed00), META, DATA and CODE folder in it)
5. If you have downloaded the USA version of the DLC, its folder name will be aoc0005000c1010ec00, just rename it for aoc0005000c1010ed00 to work with the EUR version
6. Put the SD card in your wii u and load loadiine gx2 mod
7. Select mario kart 8, use Super Smash Bros launch mode (as it is the only mode that will load your game updated), turn on DLC support and No Legit DLC mode (only loadiine gx2 mod has this option). You have to own Super Smash Bros game to use SMB launch mode, obviously... if you don't own the game, you can install it via USB brazilian mode, it will work the same (it did to me. I've installed it on the wii u memory as i don't have an USB stick or HDD free to use on wii u)...
The brazilian USB method dont support DLC right?
I've tried both USA and EUR versions and both worked, but EUR version of the game had the "shop" button name on the main menu of the game missing, also the "200cc" name on the selection of the speed to race... i don't know if it's because i have the USA version of wii u, but the same DLC worked with USA version with no problems.
If you have any doubts... just ask.. i'm brazilian and the language i speak is Portuguese, so... I've tried my best but maybe i wasn't clear enough...
Do i have to use the Smash Bros method everytime or only once?