From Fuzzrocious:
The GREY STACHE is based upon the GGG-tuned and Civil War versions of a muff fuzz, creating one versatile guitar AND bass-friendly monster! The tone stack features the ability to scoop mids to allow a heavy, deep sound, flatten the mids for an even-keeled sound, or boost the mids for a more modern sound that allows one to punch through in the mix and drive speakers well. It’s more than just a fuzz in that if you dial back the sustain, one can achieve more of an overdrive sound.