For this achievement you will need to gain a platinum medal for each challenge in the game. Some of these challenges can get a little frustrating, but with a few tries they're much more managable. A few things to remember are that you cannot go off the track and you must finish each lap under the specified time. These will cause you to fail even if you have met the criteria to get the platinum medal. Also, the criteria for the platinum medal will only appear if you have gotten the gold medal.
Each challenge you gain a platinum medal for will get you a game card, these count towards The Gambler.