Flossie is a reindeer from the Forest of Burzee. Together with another deer named Glossie, Flossie plays a key role in the creation of Santa Claus’s gift delivery system. Noting the difficulty of moving through deep snow, the reindeer propose the idea of a sledge. They explain that they must first receive permission from their guardians, the Knooks, to pull it. After gaining consent, Flossie and Glossie are harnessed to the sledge, making the first long-distance toy delivery possible.

On the journey, they also advise on how to enter homes when doors are locked, recommending the chimney as an alternative entry. However, the reindeer return to the forest one minute after the Knooks’ curfew, prompting a threat of disciplinary action. This results in a firm decree from the Knooks: the reindeer may aid in toy deliveries only one night each year, henceforth known as Christmas Eve.