This video shows you how to get the skull that is hidden in Bad Piggies Ground Hog Day Bonus Level 1-II. If you zoom out, you’ll see a skull to the left, on the side of the mountain. Build a high enough contraption, and place the pig on top. Navigate slowly to the left. The pig should roll down the tunnel onto the skull below.
If you have a different strategy for completing this level feel free to leave a comment below.