Copied and pasted from the Smash 4 Modding Discord server:
CEMU is a Wii U emulator. For our purposes, it makes testing mods way easier! Download the latest release here: http://cemu.info/
Cemuhook is extremely necessary for the emulator to run properly on many computers, so download the right release for your CEMU version here: https://cemuhook.sshnuke.net/
Just drop the .dll files with CEMU's excecutable.
To use your mods with CEMU, place your [patch (and sound and movie if you have those) folder] in this location: