Here's what Electro Harmonix say about the Green Russian Big Muff PI:
Back by overwhelming demand in a mini package! The cult classic Green Russian Big Muff first shook the ground in the mid-1990s. Since then it has been heralded by guitarists and bassists for its devastating low-end and unique sludge and sizzle. The EHX Green Russian Big Muff creates a huge tone that is all its own, but is undeniably Big Muff.
- A faithful reissue of the legendary Green Russian Big Muff from the mid 1990s - Revered by guitarists and bassists - Vintage-correct army green chassis - Controls for Tone, Sustain and Volume - Compact and pedalboard friendly - True Bypass for maximum signal path integrity in bypass mode - 9V battery included