Write on
Instead of assigning a mask to stroke in this plugin, you draw a line at a certain position. The line drawn persists throughout your animation based on the parameters you set in the plugin. Although this is pretty cool if you have one path to follow, if you have multiple paths, you’ll need to add plugins; in “Stroke” the option exists to draw all masks.

1. Create a new comp (Command-N) with a new solid (Command-Y).

2. Draw a mask with your pen tool.

3. Apply the “Write-On” effect to the layer (found under Effect > Stylize). In order to get the brush position to follow the mask, select the mask and copy the vertices (Command-C). Then, select the brush position attribute and paste (Command-V) the vertices. The mask points become the position keyframes for the brush position. They also contain floating keyframes. All you have to do is select and drag the first or last keyframe to change the timing of the animation.

Stroke Length and Brush Spacing are useful properties. Playing around with these will immediately reveal what they do.