So I cleared all three storylines, and I got to the Final Episode. I was having a hard time beating the boss so I decided to take a break. Then it hit me: to unlock the secret ending (in Standard Mode), you need to clear the Final Episode and reports menu. I always though that what they meant by "reports" is Xehanort's reports, but when I checked the strategy guide again, I learned that I have to complete ALL the categories in the Reports Menu. Meaning, I have to complete ALL mini-games, ALL Mirage Arena stages, and ALL commands and items list. I was so bummed out.