Oscillation/feedback: your signal feeds back upon itself making noise. On the The Demon/King and other pedals with this mod, there is a knob to control the type and pitch of the feedback.
Killswitch: when you press down on the footswitch, all signal is grounded out, thus muting the signal.
Gate/boost: only available on The Demon/King. Gates the signal by sputtering and killing the signal abruptly. Reacts differently to the input signal, so if you roll back on your volume knob, it gets glitchier.
Second sustain/drive/distortion mods: via a footswitch, you can switch back and forth between two different settings (think low gain/high gain). It essentially turns 1 pedal into 2! This does not stack circuits.
Tone Bypass: via a footswitch, you can remove the tone section of the circuit from the Grey Stache, providing a more open sound.