Maybe it's a hybrid creature that has been created accidentally through some magical experiment gone wrong. It has wings, horns and hoofs and is trying to find its place in the world. It could be a really interesting main character as it would have to deal with not only the normal MLP problems but also the fact that it's different from everyone else. It could start out as an outcast but gradually earn the respect and friendship of the other characters. For example, it could use its unique abilities to save a group of ponies from a dangerous situation, which would make them see it in a new light.
Perhaps it's a story where an evil force is threatening the MLP land and the only hope lies in a prophecy about a being with wings, horns and hoofs. The story could then follow the search for this being and the journey they undertake to defeat the evil. Along the way, they could meet different characters, face various challenges, and learn important lessons about friendship, courage and magic.
Since we don't know the exact 'boy with horns story', it's hard to say. But it's likely the boy with horns is the main character.
Maybe it's an orphan girl, like Emma, who has always felt different and then finds out she has wings which are the key to her true identity. She might be from a lost race of winged people. The story could be about her journey to find her people and her place in the world.
Iron Man could be the main character. He could use his technological genius to enhance the wings. Maybe he creates a special alloy for the wings that can withstand extreme heat and cold, and also has built - in weapons. He would be constantly tinkering with the wings, trying to make them better, all while using them to fight off new threats.
Hermione could be a great main character. She's smart and curious, so if she ended up in the Wings of Fire world, she would be eager to learn about the dragons and their society. She could use her knowledge of magic from Harry Potter to interact with the new world and might even try to find a way to combine the two magics.
It could be one of the baby ponies themselves. Maybe the story could be told from their perspective as they experience the world in this new, baby - like state and how they interact with their friends and family who are now taking care of them.
Pinkie Pie could be a great main character for a 'drunk mlp fanfic'. She's already so energetic and zany that a drunk Pinkie Pie would be even more hilarious. She might start bouncing off the walls even more and coming up with the craziest party ideas.
There could be a magical creature that takes on a human - like form and has black angel wings. This creature could be a guardian of some sort, maybe of an important magical artifact. It might initially be seen as a threat but is actually there to protect the wizarding world. When Harry discovers this creature, they form an unlikely bond, and the black angel wings become a symbol of their unique relationship.
The main character is likely the man with the wings. He is probably the focus as the story might be about his experiences, his feelings towards having wings, and how he uses or copes with them. Maybe he has a name that is specific to the story, but without more details, all we can say is that the man with wings is the main character.
It could be Naruto. Since he is the main character in the original series, it would be natural for him to be the focus in this fanfiction as well. The butterfly could have a special connection to him, like guiding him on a new adventure or helping him unlock a new level of his power.