Harry would probably be cautious at first. He's used to the magical world and Venom is something completely different. Venom, on the other hand, might be curious or even aggressive towards Harry. But as they get to know each other's powers and motives, they could start to respect each other. For example, Harry could show Venom some of his magic tricks, and Venom could show Harry his physical abilities like climbing walls and super strength.
In fanfiction, Venom could interact with the Avengers in many ways. For example, he might initially be seen as a threat and the Avengers try to subdue him. But then they could discover that he has some common enemies, like certain powerful villains who are a menace to both him and the Avengers. So, they could form an uneasy alliance.
The Stargate characters are used to dealing with advanced technology and alien cultures. When they meet the Harry Potter characters, they might be initially confused by magic. For example, Jack O'Neill might be both amused and intrigued by the spells the wizards cast. Meanwhile, Harry Potter and his friends would be curious about the Stargate technology and the different worlds it can access.
The characters would interact in very strange ways. The Hogwarts students would be shocked by the Jackass crew's behavior. The Gryffindors might be initially intrigued, while the Slytherins would be disdainful. Harry and his friends would probably try to keep the Jackass guys out of trouble, but it would be difficult as they are always looking for the next wild thing to do.
Harry might be in awe of Elsa's powers at first. He would likely approach her with caution and respect, as he does with most powerful beings. Elsa, on the other hand, would be curious about Harry's world of wands and spells. They could start by sharing their stories. Harry would talk about Voldemort and his battles, and Elsa would share her experiences with her frozen kingdom and her isolation.
Hermione would likely be very curious about Anastasia. She might study her as if she were a new and interesting magical creature. Hermione would probably ask Anastasia a million questions about her Muggle life and try to understand how she thinks.
The Ghostbusters would probably be really confused at first when they enter Hogwarts. They might start trying to figure out how all the magic works. Harry Potter and his friends would be equally curious about the Ghostbusters' equipment. Hermione would probably be asking a million questions about how the proton packs work. And the Ghostbusters would be shocked by things like the moving staircases and portraits that talk.
Chuck would probably be very curious about the magical abilities of the Harry Potter characters. He might be in awe of Dumbledore's wisdom and power. Harry, on the other hand, would be intrigued by Chuck's knowledge of the supernatural. They would start by asking each other a lot of questions. For example, Chuck would want to know how magic works, and Harry would be interested in Chuck's view of good and evil in his world.
Harry might be initially terrified but then use spells like Stupefy to try and stun the Xenomorphs. Hermione would probably research about them in the Hogwarts library to find a more permanent solution.
Harry would likely be both curious and cautious when interacting with Death. He might ask Death many questions about the meaning of life and death in the wizarding world. Other characters like Hermione and Ron, if they are involved, would probably be very worried about Harry's interaction with Death and try to protect him or convince him to stay away.
Harry Potter would probably be initially cautious around She - Hulk. He's used to magic and magical creatures, but She - Hulk is a whole new level of different. However, as he gets to know her, he would respect her strength and her sense of justice. She - Hulk, on the other hand, would be amazed by the magic in the wizarding world. She might try to learn some spells and would be very protective of Harry and his friends, just like she is in her own world.