I have worked in this film as a Rigger. The main changeling part of rigging the characters in this film was to maintain the bulky shape of the characters(specially the fat one) which I took care of . This was doe with help of muscles paint.
Technique :- A nurbs model was created for the torso and the hip portion and was skinned with the joint structure. Then this nurbs was treated as a muscle and was skinned with the main body.
This helped me to maintain the shape of the stomach and the hips while bending all over till maximum angles. Blend shapes were also used over muscles shaped nubs to give an extra bulge.
I also wrote scripts for automation of the rigs of props and cloths which required long time repetitively rigging, which helped us to save time.