Bad Piggies Rise and Swine Level 2-18 can be 3-starred using a single contraption. Build a three frame cart with the grappling hook in the back. Use the plunger to pull the contraption up to collect the star, then let it roll down to the finish line.
If you have a different strategy for completing this level feel free to leave a comment below.
I found the speed test easier to do using a single box contraption. wheel on bottom, wheel on left side, plunger on right side. The contraption will fall on to two wheels. Fire plunger and as soon as it pulls tap to release. Your piggie will race down the first slope to victory.