What kind of effect is that? How can I replicate it?
This is a very simple animation, actually. Here's how you could do it the easy and cheap way:


Create a solid with the size of your composition
apply "fractal noise" to it
Set the transform, brightness and contrast of fractal noise so that you have small drops instead of large shapes. You might want to set the complexity to one and experiment with the settings until you like the look.
Click the stopwatch on the brightness and lower it so much that the solid is completely black
go forward about 2 seconds and raise the brightness so that the entire solid is completely white.
Now create a text-layer under the solid and type your text
Set the "Track Matte" of your text-layer so that it takes a luma-mask from the solid above


Now, the luminance of your animated solid determines the alpha-channel of your text-layer, making it appear piece by piece. However, the effect looks sort of cheap in my opinion. For a better result, I would recommend you try to use a particle simulation (such as particular, not a free plugin unfortunately) and use the text layer as your emitter. You let the Text dissolve into dust like in avengers, and simply reverse the sequence, so that the text is being built from dust.

I hope I was able to help, have a wonderful day :)