With the opacity en scale keyframes you can let something appaer from 0 to 100, but it is always the whole layer at once. I would like to know whether it is possible that the layer appears from the bottom to the top. For example: if you have a layer with character, can you let the character appear with first the feet, then the legs, then body en then the head?
Here there is a link to kind of what i mean
(it's start at 3:50) (sorry very old movie but the only one i could think of that has the example)
yep, an animated mask would work. another simple way would by to use the linear wipe effect.
yet another would be to use a layer as a track matte... the track matte move up to reveal the layer bellow it, or the tack matte could matte just the shape, and then the layer bellow could move up to look like it was filling it...