Friday the 13th is often considered by those who believe in superstition to be a day of bad luck. Piper Halliwell was once a big believer in superstition, and would do everything to avoid bad luck.
- "Fear always comes back!"
- —Barbas' final words before being banished again.[src]
Barbas could come to earth once every thirteen-hundred years on a Friday the 13th. He would feed on the fears of witches and had to kill 13 unmarried female witches before the strike of midnight to break free of his eternal bonds of Hell, to walk the earth for eternity.
However, during the 21st century, he found other ways to break free from these eternal bonds. He would make deals with other demons or other beings, such as the Tribunal. He no longer was restricted to the once every thirteen-hundred years-rule and could come to earth on any given moment.
The only way that Barbas could be banished back to Purgatory was by overcoming your fear. A witch's power would not work, as they would be paralyzed when Barbas faced them with their fears. In 2004, Phoebe and Paige made a potion that could banish Barbas. They figured that to overcome their fear, they had to realize their biggest desire, which was to protect their nephews from him.
- The fear of Friday the 13th is called "Paraskavedekatriaphobia". It is a form of "Triskaidekaphobia", fear of the number thirteen.