The Electro-Harmonix Polyphonic Octave Generator 2, or EHX POG 2, is, as its name suggests, an octave generating pedal. It will produce 1 or 2 octaves below the input note and 1 or 2 inputs above the input note. It has a dedicated mixer for each octave and for the dry input, so you can mix these octave however you like, including by leaving any of them out. You can also mute the dry signal.
Here’s an example of this pedal in action on 12/30/17 at MSG:
Note that when Trey first engages the pedal, it’s set to an octave harmony setting, and you can hear both the input note and the octave down. Then a few seconds in, Trey reaches over and taps the pedal a few times with the palm of his hand to change settings and it switches to a setting where the input note is muted and the octave and 2-octave down harmonies are dialed way up.
You may also notice that the second sound Trey dials in has a bit of a volume swell at the front end, such that you can’t really hear the guitar attack. That’s because there’s also an effects mixer on the right side of the pedal that allows you to dial the attack down so that the note gradually fades in, like an old Boss Slow Gear pedal. The result is almost like a he’s playing a bass or cello with a bow. It’s orchestral, spooky, slightly evil, and very cool.