I have to confess, if I had to pick my all-time favourite comic book superhero of all time, then more often than not, I'd pick Batman. Maybe it's because he is wholly human, and has merely pushed himself to the very limits of what a human being can do. Or maybe it's because of his iconic rogues gallery. Or maybe it has some of the best adaptations to movies, television and video games (and, sadly, the worst). Meshing the Batman franchise with Harry Potter isn't so far-fetched. Harry and Batman share a tragic backstory, their parents murdered when they were young.
In this story, Harry Potter will be the son of Poison Ivy. This is a route other authors have travelled, many having Ivy adopt Harry, or else have her be his biological mother, and Lily an adoptive mother or surrogate. But this is the first fic, AFAIK, to have Poison Ivy and Lily Potter the one and the same. Well, save for a rather dark and bleak one-shot called Interview by whitetigerwolf (EDIT: And, as of April 13, 2017, I have been told by siblingloveF2 of at least one other: A Late Autumn Dream by Rose Midnight Moonlight Black). This story will be set ten years ahead of Harry Potter canon, with the events of this story taking place in 2005. There will be Dumbledore-bashing, that is, an evil Dumbledore. Probably no Weasley-bashing though.
BTW, this story is one of the graduates of The Cauldron, alongside another Batman crossover (specifically with Batman: Arkham Asylum) called Yin and Yang, and a Hellsing crossover, The Uncertainty Principle.
Anyway, time for the disclaimers. Firstly, this is an M-rated work for various reasons. Sex, violence, dark themes, and the Joker's sense of humour. You have been warned.
Secondly, there will be a number of annotations, and I don't want to hear any bellyaching.
Thirdly, there will be spoilers for the Harry Potter books, and for the Batman franchise. I will be playing a bit hard and fast with the Batman continuity though, so no complaints about continuity. In addition, Poison Ivy will be acting somewhat OOC, though given that she had regained memories as Lily Potter, it's justifiable.
Finally, this is a fan-written work. Batman, Harry Potter, and the characters and scenarios are property of their respective owners. Please, support the official release. Otherwise, Joker will put a smile on your face…whether you want it or not…