All Venues:
Hold L1 + Triangle and press Left, Up, Up, Right, Down, Down, Right, Down at the main menu.Tiny Players:
Enter TRIANGLE, SQUARE, LEFT, RIGHT, RIGHT, DOWN, LEFT at the main menuAll Stages:
Enter LEFT, UP, UP, RIGHT, DOWN, DOWN, RIGHT, DOWN at the main menuUnlockable Clothes:
Thanks to Revolution Readers Philo and gustavo!
Hold and L1 and TRIANGLE and enter RIGHT, RIGHT, LEFT, UP, UP, UP, DOWN, LEFT at the main menu