/shared2/menu/FaceLib/RFL DB.dat

The correct title of this article is /shared2/menu/FaceLib/RFL_DB.dat. It appears incorrectly here because of technical restrictions.

See also Wiimote/Mii_Data

Anyways, this is the database-file where Mii's are stored. It's only a signature and then Mii entries, they look exactly as they did in the Wiimote, you can extract your Miis from this file and open it up on your PC in those Mii-editors.

Any modification (even valid modifications like changing height) causes an error to appear on the screen. This error does not occur when running in Maintenance Mode, but it is the same kind of message like the one that says "Wii in Maintenance mode, Message Board will not be available.", so it could just be a bug or something.

I would say it's safe to mess around with this file though, because they have a reset function, so you can reset your file back to its default state (remove all Miis) if something goes wrong. I made a backup and I was able to restore it when the error appeared. If you reset the database (from the Mii channel) you will lose your Wii Sports and Metroid Prime 3 save, so do a backup to make sure.

I've tried the following Wii-games which are dependent on Miis, while the database was invalid, Metroid Prime 3: Corruption and Wii Sports. (feel free to add to this list) Both games gave me an error, and returned to the Wii Menu.

I don't know how they notice that the file is changed, maybe it's signed or maybe I did something wrong (but restoring worked so..).