The Draugar (S04E06)

On Halloween night, Dwight, Gretta, and Baldric are having a blast at the Woodside High Halloween bash. However, their fun takes a dark turn when the authorities inadvertently disrupt the magical barriers Baldric created to ward off malevolent forces. As a result, a swarm of the undead emerges, intent on finding Gretta to resolve some lingering grievances from the past.