How to create a simple 2d face rig in blender (2020 update)

mv.artz writes:

This is an update on how to create a simple face rig for your characters in Blender. I've been using this setup for a couple of years now and found a few extra tweaks to make the face rig extra animator friendly.

In freelance work, but also in the studio I work for, I have to switch quite often between styles.
It’s useful to me to have a couple of facial expression styles to choose from. So that I can vary these on a client-by-client basis.

One of them, this one, is a 2d projected mesh on the head, while this is relatively easy to set up, you’re still able to express yourself through the characters.

It might be a more stylized look however, the alternative would be modeling a 3d mouth and interior, and rigging that could be too time-consuming for a particular job.