Kingdom Hearts 3D: Dream Drop Distance/Secret Ending

Requirements

 * You cannot get this ending in Beginner mode.
 * In Standard mode, retrieve 7 or more trophies.
 * In Proud mode, collect 5 or more trophies.
 * In Critical mode, beat the game.

How to get this ending
After you beat the Armored Ventus Nightmare, Riku will take Sora's Keyblade. Then Riku opens a keyhole leading to the Destiny Islands where you will be questioned by three people: Roxas, Ventus, and Xion. Answer their questions correctly.
 * For Roxas, select "Losing something that's important".
 * For Ventus, select "My close friends".
 * For Xion, select "To recover something important".

When that is done Sora will go into dive mode. After the credits, gather each gold letter to spell out "Secret Message Unlocked", then save the game. You will have the secret message after the credits are done. Return to the file, open the menu and it'll say you unlocked a secret movie in the Mementos menu, which means you now have the Secret Ending you have been looking for. Go to the Mementos menu to watch it.