Print with PLA, 70% gyroid infill, fuzzy skin, organic supports. 0.24mm layer height (does not really matter, but high layer makes fuzzy skin more playful in my opinion).

There is captive tear-shaped ball printed inside, you need to break it loose using tiny screwdriver after printing. This inner ball rattles and makes the movement of the ball even more chaotic. Important part is also the excentric geometry that shifts the center of gravity when printed with high infill ratio. This makes the ball take unexpected turns as it rolls over hardwood flooring or table. (might not work that well on carpets and similar...).