Hostages

Hostages are characters in the Batman: Arkham Series who were taken by villains and/or super-criminals. These characters could be killed by their captor, however, this will result in a game over.

Batman: Arkham Asylum
In Asylum, some specific characters are taken hostage by a few super-criminals. The list of hostages are:
 * Mike the guard - After Batman entered the Patient Pacification Chamber inside the Intensive Treatment building, he sees Mike being strapped to an electric chair in the middle of the room by Victor Zsasz. Detonator in hand, Zsasz threatens to shock Mike to death shall he see Batman or anyone else getting too close. Shall he spot Batman, he will push the button and proceed to shock Mike to death as he screams in agony, which will result in a game over. Batman saves Mike by either dropping down and taking him down silently or glide kicking him and knocking him out on the floor.
 * Penelope Young - She is taken hostage two times throughout the incident. In the first part, Joker has sent henchmen to keep an eye on Dr. Young in the X-Ray Room within the Medical Facility. Under the orders of Joker, they have the order to kill Dr. Young shall anyone enter without their consent. Shall they spot Batman, one will proceed to shoot Dr. Young dead. Batman saves her by blowing open the two weakened walls, which knocks out all of her captors. She is then captured again by Victor Zsasz inside the Arkham Mansion. After Batman has walked into the Warden’s office, he spots him dragging Dr. Young further into the office, where he holds his knife right near her, threatening to kill the doctor shall he get too close. Shall Batman spook him, has Zsasz spot him, or take too long to stop Zsasz, Zsasz will proceed to stab Dr. Young. Batman saves her by knocking Zsasz out with his Batarang.
 * James Gordon - Near the beginning, Gordon was captured by Harley Quinn and Frank Boles, which they take him out of the building, with Boles being betrayed and killed. Harley then takes Gordon to the Medical Facility, which she holds him at gunpoint. If Batman is spotted by Harley’s henchmen, she will proceed to shoot Gordon dead with her assault rifle. Batman saves him by knocking Harley out and untying him.
 * Arkham Library Hostages (not kill-able) - The Arkham Library hostage’s within the Arkham Mansion was captured by Joker’s henchmen and tied near a gift box which Joker claims to be filled with gas. However, if Batman takes too long to save them, Joker wasn’t actually planning on killing them as also shown if Batman disarms the gift box, which turns out to be a boxing glove-in-a-box which almost punches Batman, but he dodges it.
 * Louie Green and an unnamed guard - During the incident, Harley Quinn had Louie Green and a fellow guard tied up by their hands and suspended over an electrified pool of water in the Guard Room. If Batman cuts their roles before turning off the electricity in the pools, they will be electrocuted to death as they stand and scream in agony, which results in a game over. If the times for the gas expires, everyone (except Harley as she is in an office) will die from the gas being unleashed into the room, which also results in a game over. Batman saves guards by shutting off the power for the electrified pools and cutting their ropes while also deciphering the door pad in order to for them to escape the gas.
 * Aaron Cash, Zach Franklin, and an unnamed guard (not kill-able) - They were taken hostage by Joker’s henchmen and taken into the Records Room. However, they are simply just NPCs that will remain tied up until Batman clears the room.
 * Aviary doctors - They were taken hostage by Joker’s henchmen and put in droppable bird cages suspended over a deep pit in the Aviary of the Botanical Gardens. If Batman knocks out a henchman before taking down the operator or gets detected by the henchmen, the operator pulls the switch to drop the doctors to their deaths. Batman saves the doctors by taking down the operator and clearing the room, only for them to be killed by more henchmen while Batman was battling in the secret facility.

Batman: Arkham City
Unlike Asylum, hostages are seen throughout some areas in City. If a henchman is nervous or terrified, they can capture and hold their hostage gunpoint. Shall they spot the player, they will shoot and kill the hostage, which will result in a game over. It is required to save them shall they be captured again. After the room is secure, the hostage will stay for a while until the player leaves the room. However, there are special characters who need to be saved and can be killed, resulting in a game over.
 * Catwoman - Catwoman was taken by Two-Face while she was looting his vault at his campaign office and is seen hanging by her feet above an acid tank inside the Solomon Wayne Courthouse, where she is to be dropped into and killed. If Batman alerts the courtroom of his presence and goes down the stairs while upstairs, she will be executed off-screen. Batman saves her by taking down Two-Face’s men and strings Two-Face up by his feet.
 * Stacey Baker - She was captured by Harley Quinn while inside the Medical Church and taken to the Sionis Steel Mill, where she is supposed to try and cure a sick Joker, though she is unable to, which Harley Quinn and her henchmen refuses to accept. She is taken into the smelting chamber to be tortured. She is not killable by any of the goons as she is tied up and is saved when Batman takes down every henchman in the room. She remains safe in the Steel Mill but disappears after the ending.
 * Tom Miller, Michaels, and Sanchez - They are undercover police officers taken by Penguin and each separated.
 * William North - North is one of the hostages to be taken by a henchman (during the church sequence) and the Riddler and place inside an abandoned building turned Riddler Room in Amusement Mile. He is placed inside a game that is like “3 Cups”, where the player must watch the cup carrying an object move around and choose it, but Riddler rigs this game. If the player attempts it the old fashioned wya or chooses wrong purposely, North will be burned alive by flame jets from the ground while on his gurney. He is saved when Batman uses his Detective Mode to figure out which cup North was in and rescues him.
 * Medical staff - They were all taken by Riddler and put into abandoned buildings turned Riddler Rooms. Most of them is not killable and is saved when Batman figures out each room and rescues the hostage.
 * Aaron Cash and several other guards - These people are the final hostages of Riddler, who are being held hostage inside Riddler's hideout below a bridge in the Bowery. They are strapped to some sort of machines that drags them along a track with a light sensor that alerts Riddler of anyone's presence. If Batman stands in anyone's way, they will explode and be killed. Batman saves them by avoiding them and taking down Riddler while putting him onto one of the machines and forcing him to walk around endlessly, while bluffing that the detonator works, though it was disabled by Batman.

Batman: Arkham Origins
Hostages are seen throughout a few areas in Origins. Like City, if a henchman is nervous or terrified, they can capture and hold their hostage gunpoint. Shall they spot the player, they will shoot and kill the hostage, which will result in a game over. It is required to save them shall they be captured again. After the room is secure, the hostage will stay for a while until the player leaves the room. However, only a few certain characters are hostages, and they are:

Batman: Arkham Knight
In Knight, many characters, specific or not, are taken hostage by numerous super-criminals and common thugs, though most of them cannot be killed. The list of hostages are:
 * Police officer - He will be taken by militia soldiers and held inside a small building next to the Falcone Shipping Yard. If Batman does not succeed in taking down the three militia soldiers in one quick session of Fear Takedown, the screen will fade to black as a soldier is heard yelling "KILL THE HOSTAGE" and a gunshot is heard. Batman saves the police officer by taking down all of the militia soldiers with Fear Takedown.
 * Oracle - She will be taken by Scarecrow and the Arkham Knight early in the game. If Batman fails certain objectives, like losing the Arkham Knight impersonator or the North Refrigeration truck, Oracle is lost to Scarecrow. She is rescued towards the end by Batman and her father, James Gordon.
 * James Gordon - Since Gordon tries to rescue Oracle by himself, he eventually gets captured. He is eventually rescued by Batman only for him to be captured soon afterwards. Gordon cannot die at any time if Batman fails. He is saved when Batman surrenders himself to Scarecrow towards the end and takes him down.
 * Robin - He will be taken by Harley Quinn when apprehending the last infected victim. If Batman fails to takedown Harley, she executes Robin off-screen. Batman saves him by taking down Harley. He is eventually captured again by Scarecrow towards the end as he was left in his cell defenseless. He is saved when Batman surrenders himself to Scarecrow and takes him down.
 * Nightwing - He will be captured by Penguin and held hostage in the AmerTek building that was turned into a gun cache in Otisburg right before the final part of Gunrunner. During the finale, Penguin takes Nightwing hostage one last time, threatening Batman to come any closer and he will shoot Nightwing. If Batman does not peform a Dual Team Takedown in time, Penguin executes Nightwing with a shot to the head. Batman saves Nightwing by performing a Dual Team Takedown move on Penguin with Nightwing.
 * Raymond Underhill - He is captured by thugs and held hostage in the unfinished CityVision building on Founder’s Island. He is not killable and will remain hostage until the area is cleared. Batman rescues him, but subsequently arrests him due to him ordering arsons so he could keep his fellow firefighters’ jobs.

Trivia

 * The hostage system is different in Asylum and Knight while in Origins and City, they remain the same.
 * Mike, Dr. Young, Louie Green, Aviary doctors, an unnamed Asylum guard, North, Cash, Medical officers, a GCPD officer, Commissioner Gordon, Robin, and Nightwing all have special deaths shall Batman fail to save them. These are non-canon however.