After finding the coin to be able to play Rextro's arcade game, you need to first play it and complete it one time. After completing it that first time, Rextro will let you know that you have another prize waiting for you if you can get a high score. Replay the game and finish the 5 laps in less than 2:30 to get the high score and this trophy. You will also receive a Pagie from him for completing this as well.