Fiendfyre

Fiendfyre is a seemingly unstoppable cursed fire whose flames take the shape of a fantastic variety of creatures that appear to stalk those caught in its path. It is also known as Cursed Fire. It has the capability to destroy Horcruxes. Apparently, the spell is difficult to control, though a more experienced wizard would be able to manipulate it to great effect. Vincent Crabbe tried to use the spell in The Battle of Hogwarts but it backfired and killed him.

In the Order of the Phoenix film, Voldemort appears to use it against Dumbledore, creating a giant snake of flames.