I'm not sure exactly as there are many different 'Harry Potter' fanfics. It could potentially be about a place full of snakes in the 'Harry Potter' universe, perhaps with some original characters or new plotlines involving the danger or mystery associated with snakes.
There might be some very interesting characters indeed. For example, there could be a young wizard or witch who has been lured into the snake pit by some dark force and is now struggling to survive and resist the evil there. This character could have a complex backstory, like they were once a good student at Hogwarts but got corrupted. Or there could be an old hermit - like character who lives on the outskirts of the snake pit and knows all the secrets about it, but is very reluctant to share them with others. There could also be a group of characters who form an alliance to fight against whatever evil is in the snake pit.
In addition to Harry, there could be a unique snake character that is a main character. This snake could have its own personality and motives. It might be a magical snake that has been around for a long time and has knowledge of hidden secrets in the wizarding world. Dumbledore could also be a main character as he often guides Harry in the original series and would likely do so in this fanfic as well, especially with Harry's new snake - related situation.
Hermione and Ron might also be main characters in this fanfic. They often accompany Harry on his adventures in the original series, so it's reasonable to think they'd be involved here. They could help Harry figure out the mystery of the snake.
In Harry Potter fanfic, snakes are often portrayed as mysterious and powerful creatures. They can be symbols of Slytherin house, known for their cunning. Some fanfics might expand on the Parseltongue ability, showing snakes as having complex thoughts and emotions. For example, a snake could be a secret ally to a character, helping them navigate the dangerous corridors of Hogwarts or uncover hidden secrets.
There could be many interesting fanfictions involving Harry Potter and a snake. Maybe the snake is a magical creature with special powers that helps Harry in his adventures. For example, it could lead him to hidden secrets or protect him from dark wizards.
Perhaps in the fanfic, Harry is turned into a snake for a period of time. As a snake, he experiences the wizarding world from a different perspective. He has to learn how to survive as a snake while still trying to fulfill his role in the fight against Voldemort. He might encounter other snakes that are either friendly or hostile, and he has to use his wits to deal with them.
In addition to the trio, there could be characters like Draco Malfoy. He might be even more antagonistic towards Harry if he is seen as the 'Snake Boy', either out of jealousy or fear. Professor Snape could also play an important role. Given his own connection to the snake - like House of Slytherin, he might have some insights or conflicts regarding Harry's newfound snake - nature. And there could be some original characters created specifically for the fanfic who are also involved with Harry's snake - related adventures.
It's very possible. Fanfic is a place where people can play with the established characters and concepts in new ways. Maybe in this fanfic, Harry has some hidden power that makes him linked to Voldemort's snake. Or perhaps there's a time - travel or parallel - universe scenario where he becomes associated with the snake in a way that challenges our understanding of the original Harry Potter story.
It could also be a snake from the Forbidden Forest. There are many unknown and mysterious creatures in there. A snake from that forest might be more in tune with the natural magic of Hogwarts. Harry, being the curious and kind - hearted person he is, might come across it during one of his adventures in the forest and start a friendship with it.