Flicker is a PT2399 delay with the time parameter being controlled by a "flickering" LED.
(You know the ones used to mimic a candle light).
The flickering LED is always on when the pedal is on, so your delay will constantly move around randomly. But by controlling the brightness and delay time you can create anything from vibrato type effects to completely crazy sound effects.
Flicker also uses a unique bypass switching system that I call "Triple Bypass", where you have three different "modes" for turning the pedal on and off:
Short Press: Works like any regular pedal. Press to turn it on and then press to turn it off.
Momentary/Hold: If you press and hold for about 1-2 seconds the pedal will enter a hold mode. Here it will simply stay in the state it entered when pressing down the button, for however long you decide to hold down the button, and then return when you release the button.
So if you press down when the pedal is turned OFF it will stay ON for as long as you hold the button pressed down, and vice versa.
Tap Tempo Bypass: If you quickly double tap the bypass button (either when on or off) the pedal will enter the "Tap Tempo Bypass" mode. Here the pedal automatically turns itself on/off in whichever tempo you tap. So to change tempo you simply tap a new tempo.
It continuously counts time since your last tap. So if you have been in a tempo for some time and just tap a single tap, it will count the time between this tap and the last tap in previous tempo as your new tempo. With a max lenght of around 1min.
To exit "tap tempo bypass" you simply press and hold the button for about 1-2 seconds. Note that when exiting this mode the pedal will be ON (regardless if you exit in a OFF or ON state).