Scanning effect

Hi guys, so I would have a question to you. So, I want to create transition using scanning effect (horizontal line going from a head to a toes of a character). What should I do, in order to create an effect where this line, while going down, switching layer with the character to other layer. So it would act as a changer of an image.

I believe what you want is called “masking.” Here’s a tutorial:

So what you would do is to create this mask layer, and then animate the mask layer so it follows your horizontal line.

does it look like this one (or roughly similar…?)

Just remembered this post where I gave a sample for “Filling up” a shape
It could be used as base for your need