Wiimmfi

Wiimmfi is a replacement server for the now defunct Nintendo Wi-Fi Connection. It was created in 2014, by Wiimm and Leseratte.

Emulation Information
If you run into any issues, make sure you are using an up-to-date version of Dolphin. 5.0-stable definitely is too old, and older development versions of 5.0 might be as well. Wiimm and Leseratte are regularly adding features to Wiimmfi that might only have been added in recent versions of Dolphin, so if you run into trouble please update to the most recent development version.

NAND Backup
You need to use a NAND backup from a real Wii or WiiU console set up in Dolphin to be able to use Wiimmfi.

See the NAND Usage Guide for more information. Make sure you use the automatic import (Tools -> Import BootMii NAND Backup), the manual way (extracting the NAND and copying the files around) will not work.

Patch Needed
Before using wiimmfi, games need to be patched via Wiimmfi Patcher. That patcher can be downloaded here:

Just grab an ISO or WBFS file of the game you want to play, put it in the folder with the Wiimmfi Patcher, and run it. The patcher will then create a Wiimmfi-patched copy of each game you put into the folder.