Bad Piggies Rise and Swine Level 2-31 can be 3-starred using two contraptions. To beat the clock, put two boxing gloves facing right on the ground and a lonely piggy in front of them. Punch as soon as you start the level to send the piggy flying. Adding a little more weight to the contraption will usually grab the star box, but it takes some luck to finish the level. We suggest continuing to trigger the boxing gloves and use them to power forward, if possible.
If you have a different strategy for completing this level feel free to leave a comment below.