The way to fully brick is unknown but it happens as well from playing out of region games from what I remember Super Paper Mario NTSC would fully brick a PAL Wii. There was another time when trying to fix a semibrick it ended up fully bricks, also my Miidia project ended up brinking a Wii during the Channel install. You may want to check out bushings blog
UnbrickMii for a little more in depth details
