6DOF means the world stays fixed instead of the whole world moving along with you when you move forward.

For example, if there's an apple on the ground: if it moves away as you walk toward it, that's 3DOF. If it stays in place so you can actually walk up and grab it, that's 6DOF.

The code has been uploaded to Reddit. However, you need the Wii U version ROM to play, and since it was never officially released in Korea, getting a legal copy is pretty tough.