Enter the Airfield level. Once you've obtained the Airfield key, you will be able to do the "Place and Trick 6, then 8, then 10 Item" goals respectively. Once you select the goal by going through the door B (named because of the B above the door you enter on the outside of the Airfield) and then hitting circle at the skate icon, you will start to set up your six, eight, or ten items respectively. Don't set any of them up. Just choose to "Do Challenge" and then pause once you've started the challenge. Then choose to "Select Level". Choose the Airfield level again. When you start the level again, your challenges of "Place and Trick 6, then 8, then 10 Items" respectively will have been completed with no tricking.

Simply enter these codes in at the ''Cheats'' password entry screen located in the ''Options'' menu.

To get these secret characters, you have to finish all challenges, hidden and regular, on the given level.