About Matte Creation and Animation with the Animated Matte Generator
The Animated Matte Generator node converts the vector points of its source drawing into matte points. Those points can be animated, allowing you to freely morph the shape of the source drawing as your scene plays out.
You can animate the points of an Animated Matte Generator by displaying its controls in the Camera view, then moving them using the Transform tool. Moving and tweaking the contour points for an Animated Matte Generator works a lot like using the Contour Editor tool.