The word being looked for in this problem would most probably be and most likely to be the word dream or vision.
A dream or vision is a device used to tell a story, usually an allegory, within a story. This is usually utilized to establish a deeper understanding of the story or of the character or characters. This could greatly affect the plot or not. This might also pave a way as to the manipulation of the reader's or watcher's thinking of the possible outcome of the story.