Hiding texture dynamically / Smooth cutout edges

Hello! I am trying to make my black sphere disappear dynamically from bottom to top, so it will create nice appearing effect for my another sphere. I have two ways of making this:
1) Just move UV layout with some nice looking alpha gradient. I am sure this method will create effect which I need. But I will spend a lot of coding time every time I need to change something (like mask, shape, etc.).
2) Apply Unlit Transparent Cutout shader. This way is way easier, but the problem is... I have ugly cutout edge(on the screenshot), and I have no idea how I can get rid of this and makes it smoother(maybe someone have any idea?).

Or maybe Unity have better ways to do such things?

 

You could possibly also make it by using vertex colour shader, then animate by looping through the mesh vertices, changing their colour.alpha depending on the vertices location y.

 

You can just use the alpha test shader and animate the cutoff value. Just have a gradient alpha texture going from the top to the bottom and as you change the cutoff value it'll move up the object. If you're unhappy with the quality of the edge try keeping the gradient texture only 1 pixel wide. There might be noise in the texture either from your graphics program doing dithering or the compression causing artifacts, both of which making it only 1 pixel wide will avoid.

If you want to get into custom shaders you can have the cutoff edge be based on world or local mesh position, or UVs, or vertex colors, or any multitude of options. I did an effect a while ago with a black sphere disappearing using a cubemap with a bunch of gradient shapes so it looked like it was ripping apart.