Access all worlds and levels.
From the main menu, select 2-player mode. Enter the initials as hg? Quit back to the Main Menu. Start a 1-player game. In the world hub, hold Left and Right (shoulder buttons), then press Select. This will unlock and allow access to all in-game levels. Holding Left+Right (shoulder buttons) and pressing SELECT will re-lock all levels regardless of the 2-player initials.