One consequence could be that the Death Eaters no longer sense his connection to Voldemort. This gives Harry an advantage in his fight against them as they can't track him through the Mark.
In some fanfictions, Harry might use powerful ancient magic that he discovers in a hidden library or from an old wizard. This magic could be specifically designed to counter the dark magic of the Dark Mark.
If Harry Potter gets the Dark Mark in fanfiction, it would completely change his relationship with the wizarding world. He'd be instantly seen as a Death Eater, and his friends would be in a state of shock and confusion. His standing at Hogwarts would be in jeopardy, and he'd likely be hunted by the Order of the Phoenix as well as the Ministry, at least until they figure out the truth.
If a character has the Dark Mark, their relationships with non - Death Eaters can become extremely strained. Friends may turn against them out of fear or a sense of moral obligation. For example, if a Gryffindor was marked, their former housemates might not trust them anymore.
One idea could be exploring how the Dark Mark affects the mental state of those who bear it. For example, it might cause nightmares or hallucinations related to Voldemort's will. Another could be a story about a character trying to hide their Dark Mark from their friends in the Order of Phoenix, creating a lot of internal conflict and secrecy.
One idea could be that Harry gets the Dark Mark by accident and has to figure out how to hide it from his friends. Maybe he discovers that the mark has some unexpected powers that he has to learn to control.
Most of the wizarding world would probably be horrified. The Dark Mark is a symbol of Voldemort and his Death Eaters, so people would be very suspicious of Harry. They might think he has turned to the dark side.
If Harry got the Dark Mark in fanfiction, his story would take a dark turn. He'd have to face the prejudice of the wizarding community. His relationships with his friends like Ron and Hermione would be strained. They'd be constantly worried that Harry might be turning evil. And Harry would have to find a way to hide the mark's influence while trying to figure out how to get rid of it. His journey would be filled with more self - doubt and secrecy.
It could change the way the wizarding world views Snape. Since the Dark Mark is a symbol of his connection to the Death Eaters, its removal might make people see him as a redeemed figure. For example, the students at Hogwarts who once feared him might start to respect him more. And the Order of the Phoenix members might trust him even more fully.
Perhaps Harry uses some powerful ancient magic he discovers. Maybe he finds a spell in a long - forgotten book in the Room of Requirement that has the power to break dark enchantments like the Dark Mark.