The Mastotron from ZVEX Effects is a heavy silicon fuzz with a few extra tricks up it s sleeve, and part of the ZVEX Vextron series.  It s works equally well with guitar, bass and keyboards, but it totally kills it with bass!  The Mastotron has a few cool and unusual features too. 

ZVEX Effects are one of the original and best known boutique pedal brands out there, setting the benchmark with their beautifully designed and ultra creative range of FX pedals