Interact with the nearby ball. It will begin a game of fetch with the skyscale. After you throw the ball, the skyscale will catch it and throw it back to you. A small white area indicates where the ball will land, and you must stand in it to catch the ball and throw it back to the skyscale. This process repeats until you have caught the ball 12 times. It may be worth using movement skills to help. Finishing this process on all three difficulties will complete the collection.