The man could be an Animagus who has the form of a large, rideable creature. Harry might not know at first and then discovers the truth during the ride.
Well, it could be a really strange and magical adventure. Maybe the 'man' is some sort of enchanted being that can fly, and Harry Potter jumps on it to escape from danger. He could be running away from Death Eaters and this strange man - creature is his only way out.
He could be a wizard who made a deal with a powerful magical entity. In exchange for great power, he lost his face. Now, he appears in the story of Harry Potter, and his presence might be a sign of a greater, more complex plot involving power struggles within the wizarding world that Harry will eventually get caught up in.
He could be an ancient wizard who was cursed and lost his face. In the fanfiction, this wizard might be seeking a way to reverse the curse and his journey intersects with Harry Potter's adventures.
'Him' could be a centaur. In the Harry Potter universe, centaurs are intelligent and powerful beings. Harry might ride a centaur in a situation where he needs to quickly cross the forest and the centaur's speed and knowledge of the terrain would be very useful.
Another possibility is Draco Malfoy. He was always in a difficult position, being from a Death Eater family but having some doubts. In this fanfiction, he could be in a situation where he's made some bad choices and now feels like he's a 'dead man walking' as he tries to find a way to make amends or escape the consequences. He has to walk a very thin line between life and death, both literally and figuratively in the wizarding world.
In the 'Harry Potter nightmare man fanfiction', the 'nightmare man' could be a figure born out of the dark magic that has seeped into the wizarding world over time. He might not be a traditional wizard but more of a shadowy being. His identity could be a mystery at first, and as the story unfolds, we learn that he was once a normal wizard who was corrupted by a powerful and evil force. He then uses his new - found dark abilities to torment the characters we know from the Harry Potter series.
Fred Weasley could also be seen as a ladies' man. He's funny, outgoing, and always up for a good time. Fanfiction could explore how his humorous and mischievous nature draws the girls to him. He might be the type to play pranks on the girls just to get their attention and then charm them with his witty remarks.
Often, the 'nightmare man' is an antagonist in the fanfiction. He could be a figure from the past, a forgotten wizard who was once defeated but has now returned with new powers related to nightmares. For instance, he might have the ability to make people relive their worst memories in their dreams, weakening them in the real world. This makes him a formidable foe for the heroes of the story.
It could be a new dark wizard who is envious of Harry's speed. This wizard might want to steal Harry's power for himself and use it to take over the wizarding world.
There could be a non - human villain like a powerful and corrupted magical creature. It might have been awakened by the chaos in the wizarding world and decided to wipe out all the wizards except Harry, seeing him as a worthy opponent or a key to some greater power it desires.