Unmask part of a texture using another unmasking texture

Okay, I have a damage texture that covers the entire screen. The image of the game is fixed, I would like a way to make the texture of the damage appear little by little. A bit like in the worms game, except that I want to gradually make a texture appear instead of making it disappear. I want to use another texture (damage zone and shape) to indicate the pixels to be unmasked on the first one. I'm terrible at shaders.
Possible? (for mobile)

 

Yep! Search for dissolve shader.