Curse of the Banshee

"We're cursed, Siobhan. From way back in the day, before we left Ireland. Some starving bog lady ancestor stole from a banshee."

- Sinead

The Curse of the Banshee is a curse placed on the family of Sinead and Siobhan Smythe when one of their ancestors in Ireland stole from a banshee.

Specifics of the Curse
"The curse is triggered when someone wrongs you. If you want it to stop, you're going to have to kill whoever is the object of your anger. [...] The power inside you will grow. Your voice becomes a weapon that you can send anywhere in the world. Focus on your target enough and your scream will decimate them. But you will also destroy your soul."

- Sinead

The curse allows the user to draw upon the mystical, powerful scream of the banshee after having been wronged by someone, a trait that is very likely due to the women of the family also being very unlikeable. If the person who wronged the cursed individual is not killed, she will continue to strengthen the power until it becomes a weapon that can be sent anywhere on Earth, capable decimating others with it at the cost of the destruction of the cursed individual's soul.

The only known way to assuage the banshee is to kill the one who wronged the cursed individual.