Do I have to draw mask manually to key frame it?

[rileytowers]

Newbie here. I have this squiggle shape that I want to reveal, left to right, to simulate calligraphy. 

I have worked out how to key frame a mask using the pen tool. However, with such a complex shape, I would prefer to paste original shape into the mask, and then make key frames, deleting a few vertexes at each one. This would give me a lot more control over the shape of the mask than drawing it manually, and in theory this would save me a lot of time. 

Whenever I attempt to keyframe with this method, the mask does not animate, it just keeps the same number of vertexes as I have deleted. It will only animate when I draw & keyframe the mask manually. Is my idea possible?? 

[Mylenium]

Turn off the "Keep mask vertex count constant" or whatever it is called exactly these days off in the preferences. That said, your workflow makes absolutely no sense. Such stuff is usually revealed using a "spine" path and applying a stroke effect, either directly or as a track matte. Any old "handwriting text" or "logo reveal" tutorial can teach you these techniques.

Mylenium