I Was Bitten (2008)

S5E11 Billy & Mandy Save Christmas

On Christmas Eve, Billy, Mandy, and Grim visit the mall, where Mandy voices her skepticism about Santa Claus, claiming he’s merely a corporate myth. Grim, however, insists that Santa truly exists and even reveals they were college pals. Curious, they embark on a journey to the North Pole to meet him. Upon arrival, Mrs. Claus reveals shocking news: Santa has been turned into a terrifying vampire.