In the words of Electro-Harmonix:

The new Nano Bass Big Muff is the latest EHX bass guitar, effect pedal.
It delivers that huge Bass Big Muff sound in a nano-sized package. With
voicing inspired by the battle-tank green, Russian Big Muff and a
classic Big Muff Pi layout of Sustain, Tone and Volume controls, it
provides sounds ranging from a slight but satisfying grit to an
over-the-top wall of bass fuzz.