Deadly Nightshade

Lily and James weren't Harry's parents. They were his aunt and uncle. Petunia decides she shouldn't have to raise her freaky green nephew when his mother is perfectly capable of doing it herself. She tracks down her wayward sister who likes to dress up in costume and attack people with giant plants, and quickly washes her hands of the entire situation. Now, Gotham and Batman have a new young villain that they'll have to deal.