So having recently obtained a Wii U, I started playing this game and have set up a Tournament for AGN gamers that have the game. It requires a code to enter and it pretty much doesn't expire.
AGNers (ya, thats the tourny's name) : 0972-5472-2001
Details: Pretty much no limits except Mushrooms Only (I had no idea what item preferences everyone would want so I can change it or make another group if ya want something different), 150cc, no AI. Everything else is default (I think). Also, its code entry only.
If everyone wants another tourny, or has made one, feel free to share the code for it here.