The wisps first appear in the episode 'The Dark Swan'. The wisps also appear in the short film focusing on Mor'du's origins where dozens of them float around Mor'du as he rides on a horse, guiding him to a cottage on a lake where he decides to change his fate. One wisp is last seen near the end of the film where it waves at the viewers and vanishes. When Mor'du is killed, the spirit of the Prince is freed, and he became a Wisp.

The wisps appear to her again two times, to guide her to the castle ruins where Mor'du lives, and later to lead her to her mother in danger. Years later, she encounters them again, and following their path, led her to the Witch's Cottage where she receives a fate - a changing spell. She soon follows them, not knowing that she is being stalked by Mor'du, but they lead her back to her family before he can attack. Princess Merida discovered the existence of the Will' O' the Wisps at a young age while trying to retrieve an arrow in the forest. They play an important role in the story, as they can lead one to their fate and destiny! They have the appearance of small floating bright blue-colored lights. They are spiritual, ethereal beings that represent past lives.

The witch from brave wikia