This mod uses BepinEx to modify the game code, like most Unity mods.

Installing the Mod:
    You can merge the included BepInEx folder with your existing BepInExFolder (".../common/Lethal Company/BepInEx").
    Ensure LoudHornCustomizer.dll is in ".../Lethal Company/BepInEx/plugins".

Installing Custom Sounds:
    Place .wav, .ogg, .mp3 files in ".../Lethal Company/BepInEx/CustomHorn"

You're good to go.
