Buzz is a circuit bent Casio PT-87 keyboard. The four modification knobs control pitch, scrambler intensity, pitch-drop intensity, and overdrive. The scrambler and pitch-drop bends can both be switched off. The metal plate the controls are mounted in also acts as a touch-sensitive pitch bend control. A 1/8" output is provided, which can be plugged directly into an amplifier. All the sounds in this video were recorded from the built-in speaker.
Here is a diagram if you would like to try to make on yourself.