How to replicate this rain drop mask in material shader

I am working on a VR world as a solo developer for standalone headsets so I am trying to keep everything very simple and optimized. this is my third and most ambitious VR project on unreal but I have no formal training, all self-taught from internet tutorials.

I have found a material effect that I would like to copy from the standalone VR Walkabout Minigolfs latest map that uses what I am assuming is a mask built into the ground material that darkens the ground material before fading out and simulates raindrops falling and hitting the ground. Since Walkabout it is developed in Unreal Engine and for standalone VR I am assuming this should work nicely but after trying various search terms to pull up tutorials to figure out something like this the best I could do was find how to make a flashing light. I was wondering if anyone can point me in the right direction to making and applying a layer mask that will animate drops on the ground before fading out?

I am linking to a youtube clip I found where you can see the effect I am refering to (sorry its the best video I could find, you have to look on the left hand side, especially the black walls of the golf course.)

many thanks

Hey @biggdavid2811

have a look at this:

Thanks, lots of stuff to look through here