Fiona is a Dark Faerie whom lives in the Haunted Woods. She is only mentioned in the Neopedia article, "Aethia and the Battle Faerie." In the article, it's revealed that she attacked the former Battle Faerie, Valeane. She witnessed the Sword of Flame and Sword of Ice turn on Valeane, allowing her to win the battle. In the article she is shown to command a pack of creatures that growl and bear red eyes. She uses these against Aethia when she traveled into the Haunted Woods to retrieve the swords. When Aethia was deemed worthy and recieved the swords, Fiona immediately retreated.
Fiona was notorious enough to be taught about at the Faerie Academy, shown by Aethia immediately recognizing her and Aethia stating, "'They taught me all about you, wicked sister.'"