When Batman confronts or encounters them, he will battle them and aggressively defeat them; temporarily stop them from breathing and breaking their bones. They often wear make up to make them look like clowns as well as colorful outfits in Arkham City. In Arkham Asylum, some were killed by the Joker himself when Laughing Gas was released and later when testing bombs. During the events of Arkham City, the gang were engaged in a brutal gang war against the gangs led by the Penguin and Two-Face, some thugs also secretly worked for the Riddler and had managed to infiltrate the Joker's gang, they were interrogated by the Dark Knight for information about him.
Following the Joker's death many of them stayed on and accepted Harley Quinn as there new leader. While others fled and joined other gangs.
- Regular: Regular henchmen punch and kick Batman. They also may grab nearby weapons such as throwable objects and poles. They are the most common enemy and can be defeated easily, they usually come in groups.
- Armed: Armed henchmen are basically regulars with firearms who are highly dangerous. The weapons they wield Assault Rifles, Shotguns and even Sniper Rifles. They can be usually taken down through silent tactics and are the main enemies in Predator Mode.
- High Security: High Security henchmen wear red/orange suits and wield knives to kill their enemies. To defeat them, Batman must stun and then beat them down.
- Armored: Armored henchmen wear clown-like armor and can use fists or knives. Like High Security henchmen, they must be stunned and beaten down.
- Stun Rod: Stun Rod-wielding henchmen shock Batman by using the Stun Rod. To be defeated, Batman must jump over him and attack from behind.
- TITAN: TITAN-injected henchmen are powerful who have the same venom as Bane. To defeat them, Batman must throw a batarangs at them to let them charge into a wall or ultra stun them. Then the Batman must beat them down.
- Raincoat: Raincoat henchmen are thugs who are identified by them wearing Arkham Security raincoat uniforms and use them to show their Joker's security. They mainly act as snipers in watch towers but can fight through melee attacks.
- Joker: Joker is the gang leader. He is also known as the Clown Prince of Crime and planned to win both gang wars with Bane and in Arkham City. After Batman defeated Clayface, Joker died of a disease from TITAN.
- Harley Quinn: Harley Quinn is the gang's second in command. She is also known as Joker's girlfriend and thugs fear her as much as Joker. Towards the end of the events in Arkham City, the GCPD arrested Quinn with the help of Batman and Robin.
- Mr. Hammer: Mr. Hammer is Joker's Lieutenant. He is greatly strong and wields a massive hammer. He defected from the gang to his brother after Joker's death.
- Clayface: Clayface temporarily worked for Joker during the events of Arkham City. He took on the role of Joker himself as ordered by the crazed clown as well as attempted to murder Batman but was defeated and knocked into the Lazarus Pit.
- Victor Zsasz: Victor Zsasz temporarily worke for Joker during the events of Arkham Asylum. He was ordered by Joker to kill Dr. Penelope Young but was stopped by Batman and managed to escape without a trace.
- Razor: Razor was one of the many thugs who worked for Joker during the events of Arkham Asylum. As he was finishing off his Bomb, Joker detonated it and killed him.
- Bane: Bane worked with Joker three times. Once and twice was in Batman's second year as they attempted to defeat Batman and the final was where Joker released Bane for him to kill Batman but was defeated.
- Frank Boles: Frank Boles was an Arkham Asylum Security Guard which was hired by Joker to help him in his attack on the Island. As he was about to escape the Intensive Treatment, Joker murdered Boles.
Taking over Arkham Asylum
After a fire began in Blackgate Prison, Joker's men were moved to Arkham Asylum as their new prisoners under the survelliance of Warden Quincy Sharp and new Security. Joker surrendered and Batman brought him to the asylum, although the Dark Knight followed to see what the clown's up to.
The thugs who work for Joker soon broke out and began running free; killing guards and doctors in their path. They eventually got Shotguns, Assault Rifles and Sniper Rifles from the Armory and even took some staff at the asylum hostage. Batman defeated the majority of the thugs who helped in Joker's take over.
After Batman defeated the TITAN-mutated Joker, Security Guards restored the asylum as well as recaptured Joker and his gang members.
Joker, Harley Quinn and their gang members were captured by Hugo Strange's TYGER Guards and brought to Arkham City. In the imprisoning city, Strange gave both Joker's gang and Penguin's gang military equipment including weaponry and took control of the Steel Mill.
The thugs went to war with Two-Face and the Penguin on the streets, as well as fighting Batman several times but were knocked out. Batman only encountered one of Joker's thugs injected with TITAN. The thugs also temporarily controlled the Church until Aaron Cash and other innocent people took control of it.
Towards the end towards their gang leader's death, thugs rather accepted Quinn as their new leader or joined other gangs.
Harley Quinn's Revenge
After Joker's death, Harley claimed her lover's crew and changed them with a new look and name. Harley´s Gang was under 100% rule by Harley and their main objective was to avenge Joker's death. Harley's Gang used colors like red and black, and, instead of green, they had diamonds in their clothes. Harley's Gang had a sad smile, their eyes had black paint around them, and Armored Henchmen had Harley's face on their helmets.
The gang took several GCPD officers hostage, and held them in either the Steel Mill, or in the Shipyard. The gang managed to trap Batman, but were defeated when Robin came after him.
It should be noted that following the Joker's death, the thugs had gained respect for Harley. They followed Harley's orders without question, and a few even voiced concern for her mental health.
It was rumored that Harley was reuniting the old gang to join Scarecrow. Their appearance didn't change much, but instead of Armored Henchmen, Harley had Brutes with her body in torpedo on the back of their coat and she had Minigunners. Their mission was to kidnap the new Jokers and to protect Harley. They only could be seen at Panessa Studios. Harley's Gang were the only crew to not appear at the GCPD Lockup.
- The Gang seem to go through personality changes in the series: In Asylum they are sadistic, serious, murderous killers, in City onward, they are more comedic, dim-witted and incompetent while still retaining the same blood-lust.