Yes, I know this has been covered other places and I have tracked down the nabscripts plugin but, even with following the demo video, it didn't work (maybe this is a CS6 thing?)
Anyway, to be clear, I am trying to find an expression to wiggle mask vertices (on a little cloud) so it looks more "alive." If anyone could give me specific instructions (I"m terrible with expressions) on how to achieve this, I would be forever grateful.
I would do it without expressions. Instead of a mask, draw the shape in a preComp, bring that preComp into your main comp, put an animated turbulent displace effect on it, and use it as a track matte over your cloud image.
Actually, you could probably just throw the turbulent displace on your cloud image, seeing as how masks happen before effects do. In this case, any texture on the cloud would also wiggle and distort. In the previous example, just the outline of the cloud would wiggle.