Scarecrow

Taunted and bullied in his youth, Jonathan Crane vowed to overcome his fears through the study of psychology and biochemistry. Kicked out of his university for experimenting on human subjects, Crane adopted the identity of the Scarecrow and armed himself with a specialized fear-inducing gas that makes a person's deepest fears become frighteningly real. His ongoing criminal reign of terror makes him one of Batman's most psychologically dangerous foes.

Road to Arkham
An anonymous tip to Scarecrow's activities noted in the patient interviews in the form of a vial of the Scarecrow's Fear Gas was left at police headquaters. Using this, Batman was able to create an antidote. The Scarecrow was found by Batman using his Fear Gas to attack his state-sponsored psychologist. Batman apprehended the Scarecrow and locked him back up into Arkham Asylum. It was revealed that the vial came from Dr. Kellerman. Even though Scarecrow was back in Arkham, he continued his plans from a secret loft hidden in the Intensive Treatment Center, plotting his next move and even getting his hands on the blueprints of Arkham Asylum.

Batman: Arkham Asylum
The Scarecrow was one of the inmates of Arkham on the Joker's "party list." As part of the Joker's schemes, he led Batman to the Medical Facility where the Scarecrow pumped the elevator Batman was in full of Fear Gas. As Batman made his way to the bottom floor he saw the Scarecrow spraying his Fear Gas into an operating room of Arkham staff and patients, causing them to panic to the point of death. Eventually, Batman began seeing a vision of Commissioner Gordon, crying for help, before being dragged out of view. Batman found Gordon's body, and sadly tried calling Oracle to tell her he was too late. He could not contact her, however, as Barbara's voice said that the number he was trying to reach was unavailable, and to hang up. Batman then made his way to the morgue.

In the morgue, an echoing voice told Batman "You shouldn't be here!" and "Get out of here!", slowly growing louder, and creating an ominous, ghostly feeling in the air. Batman turned around and exited the room, only to find himself entering the exact same room. There lay three body bags, two of which contained his deceased parents, speaking to him, taunting him about the night they were murdered, with the Scarecrow jumping out of the third. It turned into a cat and mouse game in a surreal other world made up of elements of the asylum, where a giant Scarecrow sought out the hiding Batman. Batman was able to finally break free from the Scarecrow's hold by avoiding his assailant's gaze and shining a Bat-Signal, a manifestation of Batman's will power, at him, destroying the giant Scarecrow and ending the hallucination. Back in reality, Batman went back to Gordon, only to find that it was in fact the body of another security guard Scarecrow killed.

The Scarecrow later attacked Batman with his Fear Gas once again, after Batman destroyed Dr. Young's Titan formula. This caused Batman to relive his parents' deaths, walking down a long, never-ending hall that turned into a city street in the pouring rain. As Batman walked down the 'street', he heard his parents and a younger version of himself talking in the background, before they were met and attacked by Joe Chill, with his voice monstrously distorted. Batman then briefly took the appearance of his eight-year-old self, hearing Jim Gordon and another officer discussing the murder in the background, before Gordon himself asked the young Bruce about the criminal. The voices soon ended, and another giant Scarecrow hallucination ensued, in which Batman escaped Scarecrow's hold once more by shining a second Bat-Signal at him. This time, upon returning to the real world, Batman found that he had somehow made his way into the top of Arkham Mansion's clock tower, and was locked in.

Scarecrow used his Fear Gas for a third time when Batman re-entered the Intensive Treatment center. The toxins caused Batman to relive the starting events of the game, but with the Joker and Batman in opposite positions. Joker, Harley Quinn and Zsasz escort him through the asylum like at the start of the game. Scarecrow soon approaches them with a clip board as if he was one of the arkham doctors and states that he needs to check on their patient. He starts talking about how batman never really got over his parents death and that it left him quite insane. He then says "He's all yours Joker" and joker proceeds to shoot him. He then wakes up buried under his own grave surrounded by insane versions of himself. He then once again attempts to avoid scarecrow's gaze. Much to the Scarecrow's surprise, Batman was able to break free of the Scarecrow's hold, waking up clutching Crane himself. Scarecrow injected Batman with even more Fear Toxin, leading up to another giant Scarecrow hallucination, in which Scarecrow watched as Batman fought his army of skeletons, including two larger ones (actually Joker's thugs, two injected with Titan). Batman broke free once again, causing the Scarecrow to flee to the sewers below. Batman followed Crane there and confronted him by an underground river, leading straight to Gotham's water supply.

The Scarecrow threatened to drop a bag of his Fear Toxin into the water supply, plunging Gotham's citizens into constant terror for up to one hundred years. Before he could do anything, however, Killer Croc attacked Scarecrow from the water, knocking the toxin bag harmlessly to the ground. Batman stopped Croc from eating Crane by activating his shock collar with a Batarang, causing Croc to retreat into the water, dragging Crane with him. Scarecrow, however, apparently escaped Croc through unknown means. In one of the three alternate endings after the credits, Crane emerged from the the water by docks and grabbed onto a floating crate containing the Titan formula. The same goes for Croc, and Bane. Maybe scarecrow will return to get his revenge on the caped crusader.