Well, perhaps the female Harry Potter could have some of Poison Ivy's powers. She might use her new - found plant - controlling abilities to protect Hogwarts in a more unique way. For example, creating a living wall of thorns to keep out dark wizards.
One interesting plot point is when Poison Ivy's plant - based magic clashes with the magic of the wizarding world in Harry Potter. For example, when she tries to use her powers to heal a magically - cursed plant in Hogwarts' greenhouse.
A 'Harry Potter is Poison Ivy fanfiction' might involve a cross - over of the two universes. Harry could find himself in Gotham City and interact with Poison Ivy's plant - based powers there. Or perhaps Poison Ivy somehow ends up at Hogwarts and causes chaos with her powers among the students and faculty. It would be a mix of magic and the more scientific - ish plant powers from DC Comics, which could make for some really interesting and unique storylines.
The fanfiction could start with Poison Ivy being magically transported to the wizarding world. She finds herself in the Forbidden Forest and starts to spread her influence among the native plants there. Harry Potter, while on a patrol in the forest, notices the strange changes in the plants and is the first to encounter Poison Ivy, leading to a tense first meeting between the two.
If Harry Potter were adopted by Poison Ivy in fanfiction, his view of the world could change drastically. He'd be exposed to a more nature - centric and perhaps a darker side of magic. Poison Ivy might train him to be more in tune with the natural world around him, and he could end up using plants in his battles against the dark forces in a very different way than he learned at Hogwarts. His relationship with his friends at Hogwarts might also be affected as he'd be brought up in a very different environment.
The idea of environmentalism is also quite common. Since Poison Ivy has such a strong connection to plants, fanfictions may use her presence in the Harry Potter world to bring up issues about the care and protection of magical plants and the environment in general. For example, she might try to influence how the Herbology classes are taught or advocate for better treatment of the Forbidden Forest.
One big challenge would be the difference in their moral compasses. Harry is generally a hero who follows a certain code of ethics in the wizarding world. Poison Ivy, on the other hand, has her own ideas about nature and often goes against the law to protect it. This could lead to a lot of internal conflict within their relationship.
In the 'Harry Potter Raised by Poison Ivy' fanfiction, it's likely that Harry's personality would be influenced. Instead of the somewhat sheltered upbringing at the Dursleys', he'd be in an environment where nature and a more unorthodox form of magic (from Poison Ivy's perspective) are dominant. This could make him more in tune with the natural world around Hogwarts, like the Forbidden Forest. He might be able to communicate with the magical creatures there in a different way, using the knowledge he gained from Poison Ivy.
Well, the plot could start with Poison Ivy devising a plan to seduce Batman in order to get him to stop interfering with her environmental plans. She might use her charm and her plant - based powers to create alluring scenarios for Batman. Maybe she traps him in a garden filled with intoxicatingly scented flowers that make him more susceptible to her advances.
One possible plot could be that Poison Ivy hypnotizes Batman to make him see Gotham as a utopia of nature. She could use her powers to make him believe that the concrete jungle should be replaced with a real jungle, and Batman, under her spell, starts to work against the city's infrastructure in an attempt to 'green' it. This would put him at odds with his usual allies like Commissioner Gordon and Robin, who would be very confused about his sudden change in behavior.
One possible plot could be that Naruto is on a mission and gets transported to Poison Ivy's world. He has to figure out how to get back while dealing with Poison Ivy's attempts to use him for her own ecological goals. Maybe she sees his chakra as a new form of energy she can harness.