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

Fiendfyre was a kind of bewitched flame, capable of hunting people down despite being non-sentient. It is an immensely powerful fire that cannot be extinguished by normal or enchanted water. It is also 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, a jet of fire will shoot off and become a flaming animal.

When cast, the fire appears as a roaring, billowing noise and gives its victims only a split-second's warning. The flames are of abnormally large size and take the shape of fiery monsters and beasts such as snakes and chimaeras, constantly mutating. 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, anything whatsoever that it can burn, and is capable of incinerating anything through mere contact.

Inexperienced casters will be able to conjure the flames but will have virtually no control whatsoever 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. There is also a charm to cease the flames, but unfortunately Vincent Crabbe never paid attention in class long enough to learn it, therefore costing him his life.

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

- Ronald Weasley


 * Bellatrix Lestrange
 * Tom Riddle
 * Vincent Crabbe
 * Durmstrang boy

Etymology

 * The word "Fiendfyre" was probably 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 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. Unlike Crabbe's failing control over the flames and unseen death, Goyle died by falling into the inferno after grabbing a loose chair from climbing a mountain of old stuff. Also, Goyle's lack of control is depicted as him having trouble stopping the flames from coming out of his wand once he cast the curse.
 * 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