Distant Mountain Fog

Hi guys, Does anybody know how to make this kind of fog?

 

The witcher fog seems like it's a particle effect.
The other one seems like volumetric fog.
https://www.assetstore.unity3d.com/en/#!/content/81802
There is an asset that does it really well

 

Another way to do this, if you're artistic enough, is to make a semi realistic,
or a good enough looking fog animation, or a moving clouds animation
in photoshop/gimp. With alpha transparency.

Bring it into Unity, to be used as an animated texture, or movie texture and
attach it to a flat plane object. Then put it anywhere on your mountain and enjoy.
If you make the animation correctly, it'll look convincing enough.

Note: Making a moving clouds or fog animation, (almost the same thing)
is not as hard, as most people think. Feel free to check the net for some tuts.
There are lots of them.