Bad Piggies Rise and Swine Bonus Level 2-VIII (2-8) can be 3-starred using two contraptions. To grab the star box actually requires a double-contraption that PiGineering would be proud of! Use a small 3-box vehicle with boxing gloves atop a 5-box L-shaped cart powered by motored wheels. Speed down the ramp, allowing the smaller vehicle to continue on the higher road. Then use the boxing gloves to hop your way to the finish line. Without a motor, adjust the lower vehicle to simply tilt under the weight of the boxing cart.
If you have a different strategy for completing this level feel free to leave a comment below.