For the Masks mini-project, I started a first attempt of the animation directly on paper, by drawing three facial expressions (one underneath the other), then drawing the transitions on the right.
How it was done:
-I drew the key facial expressions at the beginning of each row: excited, worried, angry.
-I then drew nine empty faces next to them, three on each row.
-If "excited" is frame 1 and "worried" is frame 5, I went to frame 3 and figured out the middle position between the two emotions.
-I then made frame 2 to be the transition between "excited" and "so-so", and frame 4 the one between "so-so" and "worried"...
-I then went and did the same stuff (last two steps) between the "worried" and "angry" expressions.
This test made me figure out the core structure of how to do animate like this, and I'm now ready to start animating a new mask, digitally...