The interaction of their powers would be fascinating. Harry's magic could be used to heal Spider - Man if he gets injured during a fight. Spider - Man's Spider - Sense could alert Harry of any oncoming danger, even magical threats that Harry might not be aware of immediately. Also, Harry could use spells to create distractions while Spider - Man uses his stealth to approach enemies unnoticed. This synergy between magic and superhuman abilities would create a very unique and exciting dynamic in the fanfiction.
There's also 'Harry and Peter: A Different Path'. This one explores what would happen if Harry took a more active role in Peter's superhero world from the start. It delves into their relationship dynamics and how it affects the people around them, like Aunt May and MJ. It's full of action - packed scenes and emotional moments between the two characters.
Their relationship could be developed through shared secrets. For example, if Peter reveals his identity to Harry, it could create a deeper bond. They could then train together and learn from each other's strengths and weaknesses.
You can try Archive of Our Own (AO3). It has a large collection of fanfictions, including many on the Harry x Peter Spider - Man pairing. The site has a good search function that allows you to filter by tags, ratings, and more, so you can easily find what you're looking for.
A plot could involve Harry getting powers as well, not just from the Goblin formula but in a different way related to some Oscorp experiment. He and Peter then have to figure out how to control their powers together and face a new supervillain created by Oscorp's misdeeds. It would add a new dynamic to their relationship as they both struggle with their newfound abilities.
A really interesting fanfiction might explore what would happen if Gwen found out about Peter's identity earlier in their relationship. It could delve into how their dynamic would change, and how they would handle the added danger that comes with knowing Spider - Man's true self.
Well, it could also happen that Peter's Spider - Man suit technology gives him away. Maybe the Avengers have some advanced tech - sensing equipment, and when Peter is around in his suit, it gives off some unique signals that the Avengers pick up on. So, they start to look into it and eventually figure out that Peter is Spider - Man.