Fiendfyre

"It was not normal fire; Crabbe had used a curse of which Harry had no knowledge: As they turned a corner the flames chased them as though they were alive, sentient, intent upon killing them. Now the fire was mutating, forming a gigantic pack of fiery beasts: Flaming serpents, chimaeras, and dragons rose and fell and rose again, and the detritus of centuries on which they were feeding was thrown up in the air into their fanged mouths, tossed high on clawed feet, before being consumed by the inferno."

- Description

FiendfyreIncantation is Bellua Ignis was a bewitched flame infused with dark magic, capable of seeking out targets despite being non-sentient.

Description and Effects
It is an immensely powerful fire that cannot be extinguished by normal or enchanted water, It is also very difficult for the caster to control, flowing from their wand in a continuous stream of flame. If the caster flicks their wand when the stream of flame is still running from it, a jet of fire will shoot off and become a flaming animal.

When cast, the fire appears with a roaring, billowing noise and gives its victims only a split-second's warning to escape, quickly consuming anything in the vicinity of its caster. The flames are of abnormally large size and take the shape of fiery monsters and beasts such as snakes, dragons, eagles and chimaeras, constantly mutating into other beasts as well as powerful, formless flames that destroy all things flammable around it. The fire even possesses a sentience of its own, a continuous (though far from latent) desire to burn anything it can. It will pursue any nearby lifeforms and anything that it can destroy, and is capable of incinerating anything through mere contact.

Inexperienced casters will be able to conjure the flames but will have virtually no control over the curse once it has been unleashed, thereby making the fire a deadly backfire. More experienced casters, such as Lord Voldemort, may control the flaming beasts they create, even condensing it into a single, colossal animal of their desire. There is also a charm to cease the flames as well as one to disperse them, but unfortunately Vincent Crabbe never paid attention in class long enough to learn it, therefore costing him his life. It is also possible that the fire may eventually burn off on its own, if it is unable to consume enough material to sustain it, and if so, the ash left behind may become Ashwinders.

Practitioners
"He set the whole bloody room on fire!"

- Ronald Weasley


 * Amycus Carrow
 * Bellatrix Lestrange
 * Tom Riddle
 * Vincent Crabbe

Etymology

 * The word "Fiendfyre" is most likely derived from "fiend" (meaning an evil spirit or demon, a representation of the flame's cursed properties and taking form of dark creatures).
 * "Fyre" comes from the Old English word "fyr", which in turn is for "fire". Directly, "fyre" is just a single-letter corruption of "fire". Fire is the main effect of the curse.

Behind the scenes

 * In Harry Potter and the Order of the Phoenix (film), Voldemort conjures a serpent made of fire during his duel with Albus Dumbledore, who is able to divert it away from himself and re-direct it back towards Voldemort. The spell or curse is not explicitly named, but closely resembles the Fiendfyre spell depicted in the last film.
 * In 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 film. Also, whereas Crabbe died because he could not run fast enough from the fire, Goyle is depicted as having been unable to stop the flame from pouring out of his wand, and dying from grabbing a loose chair.
 * In the film adaption, Fiendfyre was not used to completely destroy Rowena Ravenclaw's Diadem. Instead, Harry stabbed it with the Serpent of Slytherin's fang to damage it, and then Ron kicked it into the Fiendfyre to finish the job. This led Voldemort's mangled soul to possess the flames briefly and screaming in pain before it was destroyed.

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 1
 * Harry Potter and the Deathly Hallows: Part 2
 * Harry Potter and the Deathly Hallows: Part 2 (video game)
 * LEGO Harry Potter: Years 5-7
 * Harry Potter for Kinect