How do you unlock poison ivy on Lego batman 2?

To unlock Poison Ivy in LEGO Batman 2: DC Super Heroes, you need to progress through the story mode until you reach the level "The Riddler." After completing the mission, you can then find her in the open world of Gotham City. Look for her character token, which is usually located in a specific area, and collect it to unlock her. Once unlocked, you can switch to her character in free play mode.