Trouble masking dynamic objects


In my current project I’m building a waterfall. Each drop in the waterfall is generated from the class and added to the stage via addchild. Now I have a mask that I want all of those drops to use however I can’t seem to get this to work. I’ve tried placing the mask on the timeline and I couldn’t seem to access the mask from the file. I’ve also given the mask it’s own class and added it dynamically to no avail.

Any suggestions?