In a fanfic, Hagrid could be one of the first to encounter Slenderman in the Forbidden Forest. Hagrid's knowledge of strange creatures might make him think he can handle Slenderman, but he quickly realizes this is a different kind of threat. Meanwhile, the students at Hogwarts might start having nightmares about Slenderman, and Harry and his friends have to figure out a way to stop these nightmares and deal with Slenderman. Neville could also play a role, perhaps using his knowledge of plants to try and create some sort of defense against Slenderman.
Well, Ron might be initially terrified of Slenderman. But when his friends are in danger, he would step up. The Weasley twins could try to play pranks on Slenderman, not fully realizing the danger at first. Dumbledore, on the other hand, would be very cautious. He might observe Slenderman from a distance, trying to understand his nature before taking any action. In a 'Harry Potter and Slenderman fanfic', these interactions would create a lot of interesting scenarios.
Chapter 851, "Peace Charm", is the clearest early answer because it turns Shi Lei's situation into a concrete plot event. It opens with She initially came with the expectation of becoming the Gu Family's... and closes on The Old Madam also looked at Jiang Li..
The best chapter pointer here is Chapter 15, "The Autistic Teen Jiang Shixu". It opens with Jiang Shixu woke up from those nightmares filled with blood and darkness,... and closes on Since she didn't move, Jiang Shixu also stayed put, and the kitchen, which....
Chapter 922, "The Good Deed You Did!", is the clearest early answer because it turns Rong Kexi's situation into a concrete plot event.
Chapter 570, "A Simple Auto-Attack Baits Out an Ultimate from the Enemy", is the clearest early answer because the buildup finally cashes out in a real clash. It opens with What the heck is that?" "?? and closes on It was impossible for Jiang Li not to know; her family had been....
A practical answer is Chapter 8, because it turns the idea into a concrete scene. The chapter opens with The resentment that had barely calmed among the crowd surged back two..., adds pressure through Why keep harping on the fact that he wasn't a decent man?, and ends on Other people with a.
Chapter 613, "When a Whale Falls, All Life Thrives", is the clearest early answer because it turns Shen Lan's situation into a concrete plot event. The chapter gives readers a real answer by opening on Hearing He Wen's words, Shen Lan was so excited she nearly sprayed...
Chapter 730, "How Can You Make a Deal with a Madman?!", is the clearest early answer because it turns Don's situation into a concrete plot event. The chapter gives readers a real answer by opening on Xu Ning's emotions grew more intense as she spoke.
Chapter 687, "How Did She Die Again?", is the clearest early answer because it turns Protagonist Group's situation into a concrete plot event. The chapter turns that into something concrete by moving from In the process of pursuing the Protagonist Group, she gradually came... to I'm busy here;
Chapter 693, "Is a Man's Prime That Short?", is the clearest early answer because it turns Gu Yu's situation into a concrete plot event. The chapter gives readers a real answer by opening on Zhao Lang had never anticipated that the bravado he had shown earlier...
Chapter 876, "Gu Family's Future Granddaughter-in-law!", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. The chapter gives readers a real answer by opening on Early on the second day, Jiang Li went to the film crew.