In the words of Electro-Harmonix:

EHX has resurrected the legendary Bad Stone Phase Shifter. With prices
of 1970s vintage Bad Stones soaring, now is your chance to get a
reissue that is faithful to the original circuit design and three-knob
control layout, but features up-to-date enhancements for the modern
player.

The Bad Stone delivers an incredible six stages of phase shifting plus a
manual mode that lets the player freeze the phase. Its Rate knob
controls the phase shifting speed which goes from a very slow swoosh to a
rapid, oscillating warble. Feedback determines the depth of the phase
effect and a toggle switch lets the user select Auto or Manual modes.