Final answer:
The supernatural elements in the Perceval excerpt from medieval romances serve to build atmosphere and contribute to the plot of the story.
Step-by-step explanation:
The Perceval excerpt from medieval romances incorporates mysterious and fantastic events to create a captivating atmosphere. These supernatural elements serve both to build atmosphere and contribute to the plot of the story. For example, in the excerpt, Perceval encounters the Fisher King and witnesses the mysterious procession of the Grail.
The supernatural elements are essential to the plot as they play a vital role in Perceval's quest for the Grail and his personal growth as a knight. They also serve to build atmosphere by creating a sense of wonder, magic, and otherworldliness.