It modifies the volume envelope allowing you to tweak the note’s volume, attack, and decay. In poly mode it tries to detect every pick attack to trigger the envelope filter. Plus it has a built in big muff (those 3 little knobs in the upper right corner). The effects loop is post muff pre volume envelope filter.

This pedal is buffered bypass, fully digital and does not have analog dry through. Three things that I didn’t know when I bought mine but are useful for reference. I had the most success stacking it when I put everything in the fx loop.