>>1012383
Most models emulating a 2D style simply make normals around the face flat. Because it's too much work to craft the normal masks required to handle all the various angles. a camera might view the face in.So it's easier to just remove the shading.
>>1012388
>>1012340
It shouldn't take 4 months to create that short length of animation. And if I recall, that artist actually uses grease pencil to draw the smears and other minor details. So it still comes down to drawing to really sell the look.