A form of Dark magic, Fiendfyre was a curse that created magical flames of huge size and heat. Incredibly destructive, Fiendfyre often took the shape of enormous creatures such as serpents, dragons and birds of prey. The flames could not be extinguished by normal or enchanted water and once cast the curse was very difficult to control, multiplying and growing in power and strength. Vincent Crabbe lost control of the spell in the Room of Requirement, destroying most of the contents of the Room of Hidden Things including Ravenclaw's diadem.