One popular trope is the 'fish out of water' where Tony Stark is suddenly in the magical world of Harry Potter and has to adapt. Another is the 'team - up' trope, where they join forces to fight a common enemy, like a dark wizard using technology in a bad way.
The 'mystery connection' trope is also seen a lot. This is where there is some hidden link between the two characters, like a shared enemy from the past that they don't initially know about. As they uncover this mystery, their relationship evolves and they become closer, whether it's as friends or something more.
The 'family - like bond' trope is often seen. De - aged Tony forms closer bonds with the people around him, almost like a family. They protect him and he in turn, uses his genius to help them. For instance, he might become like a little brother figure to some characters. And there's also the 'coming - of - age' trope even though he's already an adult. He still has to grow in this new de - aged state, learning new things about himself and the world.
One popular trope is the 'Opposites Attract' in fem Tony Stark and Thor fanfiction. Their different personalities, with Tony being a tech - savvy human and Thor a powerful Asgardian god, make for an interesting dynamic.
In 'Tony Stark x OC fanfiction', a popular trope is the 'fish - out - of - water' situation for the OC. When the OC enters Tony's world of high - society and advanced technology, there are a lot of comical and interesting situations. For instance, the OC might be overwhelmed by the grandeur of Stark Tower. Also, the 'redemption' trope can be seen, where the OC helps Tony deal with his inner demons, like his fear of losing those he loves, which was prominent after the events of 'Avengers: Infinity War'.
Another popular trope is the 'power couple' idea. In the fanfiction, Female Tony Stark and Thor combine their powers and intellect to become an unstoppable force. They take on the biggest threats in the universe together, and their relationship is not only about love but also about mutual respect for their abilities. This trope often shows them in epic battles, using their combined skills to save the day.
At the start, Tony could be a bit skeptical of Harry's abilities. But when Harry shows off a spell, like making a Patronus, Tony would be impressed. They would then start to work together. Harry could use his magic to help Tony get into places that are otherwise inaccessible, and Tony could provide Harry with some cool gadgets. For example, Tony could give Harry a device that helps him communicate with the wizarding world more easily. They would learn from each other and form an unlikely friendship.
It depends on the situation. In the wizarding world, Harry Potter would be more powerful as he can use magic which is a fundamental part of that universe. He can cast spells to defeat enemies, protect himself and others, and manipulate the environment around him.
One popular trope is the 'Genius Rivalry'. Your OC can be another brilliant mind who either clashes or collaborates with Tony Stark. It adds a lot of tension and interesting exchanges. Another is the 'Underdog' trope. Maybe your OC is a new recruit to the Avengers with no real super - powers but a lot of heart and determination. They have to prove themselves to Tony and the others. 'Love Interest' is also common. Your OC could fall in love with Tony, or vice versa, which can lead to some sweet and sometimes angsty moments.
In 20 years of Harry Potter fanfiction, there are several popular tropes. The 'Powerful!Harry' trope is quite common. Fans like to write about Harry having even more power than in the books. Also, the 'Soulmate' trope is popular, especially when it comes to romantic pairings. And the 'Dark!Hermione' trope has emerged, where Hermione takes a more morally ambiguous or even dark path, which is an interesting twist on her character.
The 'Power Transfer' trope is often seen. This is when a character from one series gains the power or ability from the other series. Say, Harry getting the ability to see ghosts like Sam does in Supernatural. And then there's the 'Shared Enemy' trope. A threat that is dangerous to both the wizarding world and the Supernatural world forces the characters to cooperate, creating exciting storylines.