It will be easier to explain with an example: [WIP] Fallout terminal hacking simulator - YouTube
As you can see, in the background every so often from top to bottom “wave” rushes, I want to achieve a similar effect in the gui, but the wave should go from left to right. Any ideas?
The image on which I need a “wave” if needed 
(also would be pretty cool if speed of the wave was adjustable, but it’s rather unnecessary)
You could tween the position of a ImageLabel with the wave as the picture. You can also make the wave image transparency around 0.7 to give the effect. Just my thoughts however.
You can achieve this using UiGradient too just tweening OffsetY but you just need to do the Gradient Right
Make a texture that is going from one color to completely transparent, and then move it across the screen, and when it’s finished, you wait and start over