Obviously the in/out transitions on the layer blending tool would work but this method gives a bit more control (makes for nice pulsing effects to beat tracks etc)
for a fade down..
- to your element/prop/group add a second layer. Put your effects on this layer.
- to the first layer add a colour wash from white to black (or alternatively, colour on effect, start intensity 100, end intensity 0)
- set the wash to be subtractive
- set the effects layer to normal.
re render if necessary, where the wash is white the effect should be 100% and where it's black it should be 0%
Or another way is to click on any of the effects you want to fade out, Go to layer blending and on the out transition box check fade and the time on how long you want to fade to take.
You want to use the Curtain effect on another layer on top. Set the color to White and have it act like a curtain closing top down. Then change layer blending to 1 is Mask. If it doesn't look right try 1 is UnMask.