Show or hide a layer, or fade the effect of a blur?
In other words, for a typical layer, this will 'fade it out'. For a Blur Layer set to "Straight", this will fade between the blurred version and the unblurred version of the canvas. If you want it to become less blurry, adjust the Blur Layer's 'size' parameter.
If you want to affect multiple layers at the same time, you have several options :