Create the mask on a separate track and use Pan/Crop or Track Motion to resize it accordingly. The easiest way to accomplish this would be to use the Mask tool in Pan/Crop to make the original mask over the event with the character. Then save that as a preset and remove it from the event. Now create a new event out of Solid White Generated Media on a new track above and apply the mask shape to that event. You may have to change the mask type to negative because I assume you want to create a hole. Then change the compositing mode of the upper (mask) track to Multiply (Mask). This should create a mask that you can now resize.
~jr
https://www.johnrofrano.com/