This video shows you how to get the skull that is hidden in Bad Piggies Rise and Swine Level 2-29. The skull is located to the right of the finish line. It is a little challenging to grab this skull without triggering the level to end, but a good strategy is to create a 3-box cart with small wheels and downward-facing boxing gloves. As the cart passes over the hills at the bottom, use the boxing gloves to leap over the finish line and into the skull.
If you have a different strategy for completing this level feel free to leave a comment below.