Arkham Knight Incident
After witnessing the death of Barbara behind the glass chamber, Batman thought of a way to neutralize the Fear Toxin, to cooperate with Poison Ivy since she was immune to it, he recalled. However, Ivy is not capable of producing a large amount of antidote and therefore she needs the help of the ancient root system being buried deep underneath Gotham City. The Ultra Sonic Emitter is then collected by Batman from the Wayne Tower when Lucius Fox was done working on it, but not until he has cleared the parking ground with Arkham Knight's Drones. Batman follows the scanned image to Founders' Island and unearths the plant.