The curse was advanced dark magic, and it was one of the few known substances capable of destroying Horcruxes.

What fire spell did Goyle use?

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.

Who can control Fiendfyre?

The only confirmed use of Fiendfyre is by Crabbe (Goyle in the film) in Deathly Hallows, which implies that Fiendfyre can only be stopped by its caster. But I thought Voldemort used it against Dumbledore, and Dumbledore blasted it. Voldemort used a giant snake made of fire, yes.