How to make good puddle with Decals ?

Hello. I have a problem with Decals. Can someone please give me some advice about how to create good looking puddle with decals ?

Right now I set my decal material to Deffered Decal > Masked > Stain.

I set my reflections to pure white, my roughness to pure black and my opacity to “puddle shape” texture. It is looking fine but very boring. I want some variations in depth. I thought that I can easily achieve it with Opacity mask (some grey clouds from PS or something) but “Opacity Mask” is greyed out in every decal material type :frowning:

And if I place this grey clouds in my opacity, material isn’t showing at all

How I can add some opacity depth to my puddle ? How can I make it more interesting ?

Thanks and Cheers !