Well, perhaps in the fanfiction, the Potter family has some allies that help them in rescuing Harry. For example, they might team up with some powerful but little - known magical families. Or it could be that Lily Potter has a special connection to Harry that leads them to his location even when he is hidden away. They could then use a protective spell to keep him safe from further harm.
Voldemort would likely still be a main antagonist. He is the one who poses the initial threat to Harry in the first place. His followers, like the Death Eaters, could also be major antagonists, constantly trying to get to Harry even after the Potter family has rescued him.
In the fanfiction world, Greengrass is often a Slytherin student. She usually comes from a pure - blood family, which gives her certain status and expectations within the wizarding world. In the context of rescuing Harry Potter, she might be a character with a strong sense of justice that goes against the typical Slytherin stereotype. She could have her own set of skills, like being an excellent duellist or having a deep understanding of certain types of magic that enable her to come to Harry's aid.
One common theme is the clash of different worlds. For example, when Harry Potter is rescued in a crossover with another universe, like the Star Wars universe, there's a lot of focus on how the magic of Harry's world interacts with the technology and different species in Star Wars. It's about two very different concepts trying to coexist.
One possible plot could be that Harry is wrongly accused of a crime in the wizarding world, perhaps something related to dark magic. The police, who might be a new magical law enforcement unit, rescue him from an angry mob. They then help him clear his name by finding the real culprit, who could be a Death Eater in disguise trying to frame Harry to cause chaos in the post - Voldemort era.
Perhaps there is a prophecy in both universes that foretells of a great danger that only the combined forces of Harry Potter and the Avengers can face. When the Avengers learn of this, they travel to the wizarding world to find Harry. They rescue him from an immediate threat so that they can all prepare to face this greater danger together. The Avengers could introduce new ways of fighting and thinking to Harry, while Harry could share his knowledge of magic with them.
Maybe there's a young and brave goblin named Rikkit. He is not as well - known as Griphook but is eager to prove himself. He is the first to spot Harry in danger and convinces the other goblins to come to Harry's aid. His quick thinking and courage are what make the rescue possible in the first place.
The plot could involve the goblins rescuing Harry when he is being wrongly accused of a crime in the wizarding world. They could believe in his innocence and use their unique skills and knowledge of magic to keep him safe. Maybe they help him prove his innocence later on. They might also have their own motives for helping Harry, like they see him as a key to some sort of change in the relationship between wizards and goblins.
It could be the Queen of England, as in the real - world monarchy. In the fanfiction, she might be a figure with hidden knowledge of the wizarding world and decides to use her power to rescue Harry.
Well, in this kind of fanfiction, perhaps the Queen uses her power and resources to rescue Harry Potter from a dangerous situation. Maybe he's trapped in a dark wizard's lair and the Queen arrives with her guards to save him.