Draw some splines on a solid,
set their mask modes to “none”
do a “render->stroke” effect , all paths (on transparant), lower the hardness setting.
add “stylize->roughen edges”
tweak the roughen edges, the stroke hardness and width.
You can also use a “render->scribble” instead of the stroke, use fill type “Centered Edge” and experiment.
for easier animation, set different elements (eyes, mouth) on different layers that you parent to a null.