He might use the Patronus charm. The Patronus is not just for fighting Dementors. In this fanfiction, it could be that the positive energy of the Patronus is used to heal Tony Stark's soul. Maybe Stark has some sort of emotional or mental trauma from his battles, and the Patronus charm can soothe and heal those wounds.
Another possibility is that Harry uses some of the more ancient and powerful magics. For example, the magic associated with the Deathly Hallows. If the Resurrection Stone has the power to bring back the dead in a way, it could be used to rejuvenate Tony Stark's life force. Or the Elder Wand could be used to channel powerful healing magic, perhaps by transferring some of Harry's own life energy to Stark in a controlled and magical way.
The healing magic of the Hogwarts hospital wing could be a big part of it. Harry would know about all the potions and spells used there. So he could use something like the Wiggenweld Potion, which is known for its healing properties. He could also use the 'Vulnera Sanentur' spell which is used to heal deep cuts and wounds. If Tony has any physical injuries, these could be very useful in his healing process.
One way it could happen is through the power of the Time - Turner. Harry could use it to go back in time and prevent the event that injured Tony Stark in the first place. Or he could take Tony to Hogwarts where the advanced magic and potions could be used to heal him. The magic potions like the Felix Felicis could be given to Tony to enhance his chances of a speedy recovery, and the healing spells of Madam Pomfrey could also be very effective.
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.
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.
Harry's magic is the key to Thranduil's healing. His spells can directly target the injuries or ailments of Thranduil. For example, if Thranduil has a poisoned wound, Harry could use magic to draw out the poison and then close the wound.
In fanfiction that combines Harry Potter and Tony Stark, 'petal' could potentially be used in a variety of ways. It might be part of a magical plant in the Harry Potter aspect, like a petal from a rare flower used in a potion. In relation to Tony Stark, perhaps it could be part of a new technology he's developing that has an aesthetic inspired by a petal's shape. However, without more context, it's hard to be certain exactly how it would be incorporated.
He could be a security specialist. With his magic skills like the Patronus charm which can repel Dementors, he could use similar magic to keep Stark's facilities safe from intruders. His ability to apparate and disapparate could also be useful for quickly moving around the compound and responding to threats.
Another possibility is that he uses some ancient magic that he discovers in the Forbidden Forest or some old wizarding books. This magic could be more in tune with nature and be used specifically for growing food. It might involve some sort of connection with the earth and the natural cycles of growth.
He'd be a really cool mix. He'd probably be more confident and tech - savvy. Since Tony Stark is his dad, he'd have that Stark charm and arrogance a bit. He'd still be brave like in the original, but he'd also be more innovative in his use of magic, maybe combining it with some technology.
In this fanfic, Tony Stark would interact with Harry Potter in a very interesting way. At first, he might be a bit overbearing, trying to control every aspect of Harry's life because he wants to keep him safe. But as he gets to know Harry better, he'd start to respect Harry's independence. Tony would also be fascinated by Harry's magical abilities. He might try to find a scientific explanation for it, and in the process, he and Harry would have many deep conversations. Harry would learn from Tony's confidence and self - assurance, while Tony would learn about the power of magic and the importance of things that can't be measured by science.
Yes, there are quite a few fanfictions out there that combine the worlds of Tony Stark from the Marvel universe and Harry Potter. Writers like to explore crossovers where the genius of Tony Stark might interact with the magic of Harry Potter's world. It can be really interesting to see how his technology would mesh with magic spells and wizardry.