Fiendfyre

"Like it hot, scum?"

- Vincent Crabbe, as he conjures Fiendfyre in the Room of Requirement in an attempt to kill Harry Potter

Fiendfyre (also known as Cursed Fire) is a type of fire made from Dark Magic. It is very powerful, as it cannot be put out by Aguamenti (or any normal type of water), but is very difficult for the caster to control. The blaze is so potent that Fiendfyre is one of the very few substances that are capable of destroying a Horcrux.

Fiendfyre initially appears as a "roaring, billowing noise" and gives its victims only a moment's warning. Its flames are of abnormal size and take the shape of fire-breathing monsters and beasts, such as serpents, chimaeras, dragons, and raptors, continuously mutating. It appears to have enough consciousness to actually follow its intended victims. The fire will pursue nearby lifeforms as if it were alive itself, sentient, even the one who conjured it if they lack control. The fire will also pursue anything it can burn for more fuel and seems to incinerate anything through mere contact.

It is unknown if there is a counter-curse for Fiendfyre; Aguamenti merely evaporates before touching it. Inexperienced casters will be able to conjure it, but will have virtually no control over the flames once they are unleashed, which would make the flames a potential deadly backfire, though an experienced Dark Wizard (like Lord Voldemort) would be able to control it and manipulate it to great effect.

Known uses
In 1995 the Dark Lord Voldemort used Fiendfyre against Hogwarts Headmaster Albus Dumbledore during their fight in the Ministry Atrium. It took the shape of a Basilisk.

In 1998, Vincent Crabbe learned how to cast Fiendfyre, presumably under the tutelage of Amycus Carrow, a Death Eater and professor of the Dark Arts at Hogwarts School of Witchcraft and Wizardry when it was under the control of Lord Voldemort. He was either not paying attention when Carrow discussed how to control the curse or lacked the skill to do so.

During the Battle of Hogwarts, Crabbe, Gregory Goyle, and Draco Malfoy cornered Harry Potter, Ron Weasley, and Hermione Granger in the Room of Requirement during the latter group's search for Rowena Ravenclaw's Diadem. Crabbe, who at the time rebelled against Malfoy's leadership, conjured Fiendfyre in an attempt to kill Harry and his friends, but he was unable to control it. Since the fire was used in an enclosed area, Crabbe perished in the cursed blaze. Harry, Ron, and Hermione narrowly rescued Malfoy and Goyle before barely managing to escape.

When the diadem, having been exposed to the flames before its recovery, broke apart in Harry's hands upon their escape, Hermione realised it was Fiendfyre they had escaped from. She had known that it was capable of destroying Horcruxes, but claimed it was far too dangerous for her to attempt to use.

Behind the scenes

 * In the film adaptation of the Goblet of Fire, a student from Durmstrang casts a fiery bird-like creature upon entering the Great Hall of Hogwarts School of Witchcraft and Wizardry. However, he casts the spell by blowing upon his wand, which is not explicit in the books.
 * In the film adaptation of the Order of the Phoenix, Lord Voldemort, while in a fierce and deadly duel with Albus Dumbledore summons Fiendfyre as the description is the same. It was formerly unknown if the spell were Fiendfyre, but it is sure to say it is; because the same Fiendfyre shape were used by Gregory Goyle two years later. Interestingly, he also uses his breath to cast the spell, similar to Order of the Phoenix. The spell Voldemort casts takes the form of a Basilisk.
 * In the film adaptation of Half-Blood Prince, when the Death Eaters attack the Burrow, Bellatrix Lestrange possibly casts Fiendfyre as snake figures can be seen in the fire ring striking at Remus Lupin and Nymphadora Tonks who are attempting to contain the blaze.
 * The Firestorm spell unleashed by Dumbledore in the Horcrux cave may be related to Fiendfyre, due to its intensity.
 * In the film adaption of the Order of the Phoenix, Fred and George Weasley, just before leaving Hogwarts, throws a Whiz-bang in the air and releases a massive fire dragon, this Bang may have Fiendfyre hidden inside.Fiendfyregoyle.jpg (in film adptation Gregory Goyle)'s Fiendfyre]]
 * The only time Fiendfyre is ever explicitly identified is in chapter thirty-one of Deathly Hallows.
 * In the Harry Potter and the Deathly Hallows: Part 2, Gregory Goyle uses Fiendfyre and dies instead of Crabbe. This is due to the fact that Crabbe has been cut from the films because his actor is currently in legal detainment due to a drug-related charge.

Appearances

 * Harry Potter and the Goblet of Fire (film)
 * Harry Potter and the Order of the Phoenix (film)
 * Harry Potter and the Half-Blood Prince (film)
 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows: Part 2

Notes and references
Feudeymon Адский огонь Pirunpalo