How do I move a mask?

[Graham Quince]

In the Mask options, you can keyframe the Path. This will allow the mask to move. Using the Mask path tools, you can change the shape by moving individual points, or grab the whole thing and move it.

This tutorial from Mark Simpson showed me how to animate masks (longer ago than I care to admit) and even though the software looks different now, the processes are still the same:
https://library.creativecow.net/articles/simpson_mark/tornado.php

http://www.YouTube.com/ShiveringCactus – Free FX for amateur films
https://shiveringcactus.wordpress.com/ – FX blog