Electro-Harmonix Double Muff

The Electro-Harmonix Double Muff is, as its name suggests, two chained muff transistors in one pedal. It has a very simple control layout that includes two gain knobs, one for each transistor, and a toggle switch that toggles the second muff on and off. 

This pedal has a surprisingly wide range of usable tone options, especially if you count your guitar volume and tone knobs. It can sound close to an overdrive pedal or a dirty fuzz pedal, depending on the settings you dial it to, and everything that surrounds the pedal.. including your guitar pickups, the volume on your guitar, the tone, the amp, other pedals in the chain and your heart rate. This pedal is extremely sensitive to signal path changes, for better and worse. So much that I would say that if you are using many pedals and tend to change the combination a lot during a gig, just take it off your board and leave it for studio work, because it can be a tough beast to control! However, if I judge by sound, I think this is one of the most underrated and misunderstood pedals I had the chance to play with. It is unique and it makes you play things nothing else will! It is really special in that sense in my opinion (scroll down for some sound samples).