A grumbly distortion/ring mod.
The Fredric Effects Grumbly Wolf is a highly versatile combined distortion, fuzz, octave and ring mod effect. Capable of everything from classic crunchy overdrive to intense octave fuzz madness. This is based on an asymmetrical hard clipping distortion circuit, followed by a great sounding octave/ring mod effect (based on the classic Green Ringer), which can be turned on and off with the toggle switch. This second stage can provide extra gain for full-on splattery fuzz, or clangy ring mod type sounds with the distortion turned down.
This excellent demo is by Christian at Magnetic Effects.