An SD card (FAT32 formatted) and Wi-Fi connection.
HackMii Installer v0.6 and Bannerbomb v2.A Wii running the latest Wii System Menu 4.2 (of course, Wii Homebrew is possible on older versions, but the installation process is slightly different, so for the sake of this how-to, I will assume you have the newest update).Warning: Proceed at your own risk! If you read the documentation included with the installers and use caution you will be enjoying the fruits of Wii Homebrew in no time, but be warned that if you do something silly there is always that tiny chance of “bricking” your Wii.
