Bad Piggies Ground Hog Day Bonus Level 1-IV (1-4) is 3-starred in two steps. First, navigate your contraption all the way in the tunnel, through the star box. Detonate the tnt to send the pig to the finish line above. Finally, using the same contraction, you want to detonate the tnt just after passing the second hill. That should send the pig flying high towards the finish line within the time limit.
If you have a different strategy for completing this level feel free to leave a comment below.
To get the skull, I built a rocketship on wheels with assymetrically placed boost bottles. Triggered the bottles a fraction of a second after each other, just after the contraption started to roll.
For the 2nd run (to get the 3*’s), I moved the tnt to the box under the pig after a few tries like the video with no luck getting the pig over the cliff. After the tnt move, he went in one try. That made more sense to me that the tnt in the front.