The Screaming Skull is a self-oscillating fuzz.
It has five control knobs, clear – gain – filter – oscillator – volume and three switches that change the mode of operation.

A True bypass switch turns the pedal on/off and another one turns the oscillator on/off.
There is also a toggle switch which is engaged with the filter.

It has a clean and warm fuzzy sound and when the oscillator is "on" interesting things are coming out of that.