This video shows you how to get the skull that is hidden in Bad Piggies Flight in the Night Level 4-30. The moustache skull is located above the starting point. Build a wheeled contraption with two bottom tnts, and the pig on top. Let the contraption slide down the slope and detonate the tnt when it reaches the bottom of the hill. The pig should be sent flying high to the left, onto the skull.
If you have a different strategy for completing this level feel free to leave a comment below.
I merely used a tnt on far left with pig on top, egg must be placed somewhere (anywhere but on top of pig). Fire the tnt & the pig shoots up through the space and onto the skull.