The script adds a waving movement to fogs. What it does is just to adjust the x/y speed on the fog each certain time.
It's flexible enough, letting you to define the lapse between speed changes, the change amount, and minimum/maximum values.
And it's tested on BlizzABS at least. So I suppose that heavy changes on map behaviours is not a problem.
Paste above Main. Instructions are near the start of the script.