The poisoned apple could be a gift sent by a mysterious figure to one of the characters, like Iron Man. When he touches it, it starts to release a dark magic that affects his suit's technology. Harry Potter then detects the magic and tries to find a way to reverse the poison's effects.
Perhaps a character from the Harry Potter universe who has turned bad, like a Death Eater, teams up with a villain from the Avengers world. They create a poisoned apple that has the power to turn good characters evil. The apple is then placed in a strategic location where it's likely to be found by one of the heroes. When Thor picks up the apple, he starts to become aggressive and turns against his fellow Avengers. Harry Potter and his friends must figure out how to break the spell of the poisoned apple and bring Thor back to his normal self.
In a fanfiction where the Harry Potter and Avengers universes collide, a poisoned apple might be used as a weapon by a new villain. This villain, having studied both magic and technology, creates a poisoned apple that can disrupt both magical and super - power abilities. The heroes from both worlds, Harry Potter and the Avengers, have to work together to find a way to neutralize the apple's poison. They face many challenges along the way, like dealing with different types of magic and the unique powers of each Avenger, but eventually, they succeed through their combined efforts.
The petal could be a form of communication. In the fanfic, a character from the Avengers could find a petal with a message written on it in runes from the Harry Potter world. This could start an adventure where they have to find someone who can read the runes and decipher the message. Also, the petal could be used as a tracker. A wizard could use a spell on a petal to track the movements of an Avenger.
Well, first of all, the Avengers would need to locate Harry Potter. Maybe Hawkeye could use his eagle - eyed skills to spot him. Then, Captain America could lead the team in a rescue mission. Hulk could be the muscle, smashing through any obstacles in their way. Black Widow could use her combat skills to take out any enemies nearby. And finally, they could use the Quinjet to escape with Harry to safety.
In a more literal sense, if we think about a positive battery in a fanfic, it could be a new invention. Maybe a wizard in the Harry Potter world teams up with Tony Stark. They create a positive battery that uses both magic and technology. This battery could power a device that can nullify dark magic and the weapons of villains from both universes.
One way could be through a crossover spell. Maybe a powerful dark wizard in the Harry Potter universe discovers a way to create a Rinnegan - like power. They might use it to gain ultimate control over magic, similar to how the Rinnegan gives great power in Naruto. This could lead to a new kind of threat that Harry and his friends have to face.
One way could be through a magical spell gone wrong. Maybe a spell that was meant to transform an object into a helper, like in Beauty and the Beast, but instead it affects a character in the Harry Potter universe in a similar way. For example, a student might be turned into a beast - like form and only the love of another can break the spell, much like in the original Beauty and the Beast story.
Harry Potter might save the Avengers by using his magic to teleport them away from danger. He could use Apparition or the Floo Network if he could somehow make it work in the Avengers' world.
Harry Potter could lead the Avengers through his strategic thinking. He's had to plan against Voldemort and his Death Eaters. So he could come up with battle plans for the Avengers. He might use magic to communicate with the team over long distances, like a modified version of the Floo Network. Also, he would encourage the Avengers to embrace their individual strengths, just as he did with his classmates at Hogwarts.
He could use his invisibility cloak for stealth missions with the Avengers.
Well, Harry Potter might assist the Avengers in fanfiction by providing unique forms of transportation. His ability to apparate or use the Floo Network could be a great advantage for the Avengers. Also, his experience in fighting dark magic could give the Avengers new strategies against their powerful foes.