Level 13. Unfriendly Skies (2)

In the baggage claim area, jump onto the track. When you see a red button on the right, jump off the track, push the button, and enter the open panel before time runs out.

Inside the "Impulse Gifts" shop, interact with the cash register to open a panel revealing a fortune cookie.

In a room containing 3 phones, 3 Pachinko machines, and black and blue dispenser machines, jump on the Pachinko machines, then onto the black dispenser machine. Access the open panel. If this panel is not visible, you must first obtain the red pass key from inside the airplane cabin and use it on the elevator door, then ride the elevator.

In the control room, jump on the coke machine, then jump left onto the dispenser machine. Face right and shoot the button to reveal items.

Enter the area with numerous Pachinko machines and an airplane cabin. Facing west, shoot the button on the eastern side of the three isolated Pachinko machines. Jump onto the machines and enter the open panel to find a Missile Launcher.

In the room containing a plane's engine, jump and interact with it to find a panel that opens to reveal a Rail Gun.

This secret leads to the secret level "Auto Maul" (Level 22). Locate the elevator with signs for Gate 21A and Gate 21B. First, press the button to call the elevator with its doors open. Then, if you can step out and back in, you can stand on top of the elevator. There is a switch on top; activate it to have the elevator transport you to the top, where the secret level end switch is located.