OpenWiiPax is an open-source tool to undo the code obfuscation on fail0verflow's Wii software, including the HackMii Installer and CEIL1NG_CAT.
Programs without per-function obfuscation (e.g. CEIL1NG_CAT) are fully unpacked after the main ELF is extracted from the packed binary. To do so, use the command
openwiipax unpack <input> <output>
Programs with per-function obfuscation (e.g. HackMii Installer) contain encrypted functions that are decrypted immediately before they are called. These functions typically generate analysis errors in Ghidra as it tries to interpret the encrypted data as PowerPC instructions. To fully unpack a program with per-function obfuscation, use the command
openwiipax unpackdeep <input> <output>
Note that input should be the fully obfuscated ELF (not the ELF generated by calling unpack).