Fiendfyre
An advanced Dark curse that produces enormous cursed flames in the shape of beasts, which spread of their own will and consume whatever they touch.
Fiendfyre is a curse that produces enchanted flame of enormous size and heat. The fire pours from the wand in a continuous stream, and a flick of the wand sends off a jet that takes the shape of a vast burning creature, serpents, chimaeras and dragons among them, changing from one into another as it goes. The flames have a will of their own and hunt down anything living in their path, spreading fast and consuming whatever they touch. Ordinary water does not put them out, and neither does conjured water. Controlling the curse takes exceptional skill and unbroken concentration, and a counter-curse exists to end it.
How far into Harry Potter have you read?
Set your place and this page rewrites itself to exactly that point. Nothing ahead of you will show.