Go to the option menu and set the difficulty to 'Kid Mode'. Enter the New Jersey level and go to the draining pool. Enter the pool. Make sure that you are in a regular stance. Angle towards your right. Ollie and do as many flips or grabs as you can, holding Left. When you are coming down, land sideways and you should be back in the air for a short time. If done correctly, the game will count it as one combo.