This video shows you how to get the skull that is hidden in Bad Piggies Flight in the Night Bonus Level 4-IX. The skull is located above the starting point, slightly to the left. To collect this skull, we built a “copter” on wheels with a blue rocket in front, pointing to the left. Carefully navigate your contraption through the cave and the opening above. Once your vehicle clears the gap, trigger the rocket to propel your pig towards the skull.
If you have a different strategy for completing this level feel free to leave a comment below.