By doing some experiments in anime studio, I accidentally found a way to create a 2.5D mouth mechanism.
You just need to use the program properties to folding shapes and fold them as if it were a peice of paper.
Just look at my exemples:
https://www.dropbox.com/s/uxi3pr2fcq9h2 ... .anme?dl=0
https://www.dropbox.com/s/7wqmu58n7utme ... .anme?dl=0