Well, in this type of fanfiction, Hermione could also be an important character, but in a different light. Maybe she tries to stop an evil Harry, or perhaps she is corrupted by him and becomes his accomplice. Other characters like the White Witch from Narnia could be involved. Her icy magic and cold - hearted nature could be an interesting contrast or complement to an evil Harry's powers. And don't forget about characters from other YA dark fantasy series, such as the Darkling from Shadow and Bone, who could potentially cross paths with an evil Harry.