"Travelers—particularly those who venture out after sunset on unfamiliar pathways—beware of the will o’ the wisps.
It is said—though by whom is a bit of a mystery—that on certain days for certain travelers in certain parts of the world, little lights dance on the horizon, whispering tempting invitations… pledging the answers to lifelong questions, the realization of dreams, a key to secret treasures—a change of fate.
Charmed and curious, unsuspecting travelers follow the floating lights, mesmerized by their whispers, their promises. Yet no matter how long or how fervently they follow, they never quite touch the beautiful beacons whose flickering lights eventually fade and disappear… leaving the inquisitors, the dreamers and the treasure seekers lost… and alone."
Merida discovered the existence of the will' o' the wisps at young age while trying to retrieve an arrow. She follows them, not knowing that she is being stalked by Mor'du, but they led her back to her family before he can attack. Years later, she encounters them again, and following their path, is led to the Witch's hut where she receives a fate-changing spell. 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.
When Mor'du is killed, the spirit of the Prince became a wisp. At the end of the film, a wisp watches Merida and her mother riding together on their horses behind a stone pillar. The wisp then turns to look at the viewer before it vanishes.
- Mark Andrews explained the origins of the wisps, and how they treated them in the movie:"The will o’ the wisps are in a lot of Scottish folktales. They were said to lead you to treasure or doom—to change your fate—but they’re an actual phenomenon of swamp and bog gas seeping up through the earth and interacting with the natural resources to create the blue flames. People would follow these lights thinking they were little fairies, and basically drown or get sucked down into the bogs.
- We made the wisps like actual little spirits. They’re almost like Marley’s ghost in a way, because Marley’s ghost isn’t an evil spirit—even though he’s frightening, he’s trying to warn Ebenezer to change his ways. That’s what the wisps are doing. There’s a duality to them, because they’re either good or evil—they led Merida into more and more trouble, but in the end, they’ve led her exactly where she needs to go."