Banshee

A Banshee is a dangerous Dark Creature known primarily for its powerful and lethal wail. It is a figure of fear within the Wizarding World, to the extent that it can manifest as a person's Boggart. Though mentioned in tales of heroic deeds and as a subject of academic speculation, its true nature remains largely mysterious in the canonical texts.

The only physical description of a Banshee in the novels comes from the one manifested by Seamus Finnigan's Boggart. It took the form of a woman with floor-length black hair and a skeletal, green-tinged face. The most defining and feared characteristic of a Banshee is its voice. Its cry is believed to be fatal to anyone who hears it. When Seamus Finnigan cast the Riddikulus charm on his Boggart-Banshee, its terrifying scream was silenced, suggesting the voice is its primary method of attack or the source of fear it inspires. Harry Potter once speculated that the disembodied voice of the Basilisk he was hearing in the walls of Hogwarts might be a Banshee, highlighting the creature's reputation for having a deadly, unseen cry.

Banshees are referenced on a few occasions throughout the Harry Potter series, typically in relation to their fearsome reputation.

• The Bandon Banshee: Gilderoy Lockhart claimed credit for defeating the so-called “Bandon Banshee” in his book, Wanderings with Werewolves. He boasted that the Banshee stopped wailing because it took a fancy to him. This was later revealed to be a lie; Lockhart had stolen the story from a witch with a prominent hairy chin, using a Memory Charm on her to erase her memory of the true accomplishment.
• Seamus Finnigan's Boggart: During a Defence Against the Dark Arts lesson with Professor Remus Lupin in 1993, Seamus Finnigan's greatest fear was revealed to be a Banshee. The Boggart transformed into the creature, giving students their only visual impression of one. Seamus successfully used the Riddikulus charm to make it lose its voice, which caused it to clutch its throat and look defeated.
• Basilisk Voice Comparison: In 1992, when Harry Potter first heard the voice of the Basilisk moving through the castle's plumbing, he asked Ron Weasley if it could be a Banshee.

The Banshee of the Wizarding World is directly inspired by the “banshee” of Irish mythology. The name comes from the Old Irish bean sí (pronounced “ban-shee”), which translates to “woman of the fairy mound” or simply “fairy woman.” In folklore, a banshee is a female spirit whose mournful wail, or “keening,” is an omen that foretells a death in one of the old Irish families.

• In the video game adaptation of Harry Potter and the Chamber of Secrets, Banshees appear as common enemies in certain areas. They are depicted as ghostly, floating female figures that shriek at the player. (video game)