England, Scottish Highlands.
In a remote area shielded by several protective spells, Harry was intently waving his wand, practicing the Fiendfyre Curse he had learned from Mad-Eye Moody. He lit the makeshift fire pit in front of him and tried to control the black flames, keeping the Fiendfyre from spreading in every direction.
To Harry's left, Hermione and Ron gripped their wands nervously, ready at any moment to use the counter-spell Moody had taught them not long ago to extinguish the Fiendfyre in the fire pit.
Unfortunately, all three of them failed.
Not long after Harry finished casting the Fiendfyre Curse, the black magical fire turned into rolling waves of flame. It showed signs of losing control and began to spread beyond the fire pit.
Once the black flames spread out of the fire pit, Ron and Hermione swung their wands at the same time, using the counter-spell Moody had taught them in an attempt to suppress the out-of-control Devil's Fire.
However, they only managed to suppress the black flames slightly and failed to stop Fiendfyre from spreading.
In the end, it took several Order of the Phoenix members around them working together to completely contain the surging black Fiendfyre and put it out in short order.
"Failed again."
Harry could not help feeling discouraged. This was already his third day practicing the Fiendfyre Curse.
Unfortunately, advanced Dark magic was far more difficult than they had imagined. Despite all their effort, they had made little progress.
Summoning Fiendfyre was not difficult at all, but controlling it was. It quickly went completely out of control, spreading and expanding wildly, devouring everything in its path.
Even the counter-spell Ron and Hermione were practicing had little effect on Fiendfyre, as though the supposed counter-spell were fake.
"I really don't understand why you insist