Throughout the course of the game you can unlock little films in the Theater mode where you can watch hidden videos in the game or the past cutscenes. Below is the film name and how to unlock them.

Unlockable	How to Unlock
Flying Fortress Kabula	Play through Revenge of the King
Friends and Sun	Complete Revenge of Meta Knight
Halberd Scenes 4-6	Play through Revenge of Meta Knight
Halberd Scenes 7-9	Play through Revenge of Meta Knight
Kirby's Triumphant Return	Complete Milky Way Wishes
Marx's Mad Plan	Play through Milky Way Wishes
Milky Way Wishes	Play through Milky Way Wishes
Revenge of the King	Play through Revenge of the King
Staff Credits	Complete Milky Way Wishes
To the Battlefield	Play through Milky Way Wishes