Arkham Lunatics

The Arkham Lunatics, Arkham Inmates or Behaviorally Modified Inmates were extreme mentally unstable patients of Arkham Asylum.

Description
During the events of the Arkham Asylum incident, the most hardcore and utterly deranged of the Asylum's many cases were released from their cells by the Joker. It was worth noting that after doing this, one of Joker's many taunting messages over Arkham's PA system included instructions for his henchmen to put the lunatics down on sight, which many of them failed to do. Joker seemed to have ordered their release strictly to harass Batman, but as much as he relished their madness, he was not sure if the lunatics would prove a hindrance to his plans or if they would actually be able to overpower the Dark Knight.

Living up to their name, they had no grand designs or iconic motifs but only the purest insanity that drove them. They were seemingly incapable of coherent speech and instantly attacked anything or anyone in their sight. Only unconsciousness or death kept them from attacking in an all-out frenzy capable of badly and rapidly injuring Batman, something even a single blow from a Titan Henchman could not lay claim to. They seemed to lack a significant feeling of pain and their harnesses apparently helped provide additional protection from brutal blows and even gunshots. Facing more than one in the same area could be difficult, and they were one of the reasons the "Totally Insane" Challenge Map could only be endured and never truly beaten.

The lunatics could not truly be described as henchmen or even proper thugs. Joker had no control over them and was at least careful of them. It was possible releasing them was a contingency rather than part of whatever made up Joker's original plans as conversations between Joker and Harley indicated Batman was progressing faster than Joker cared for. However, Joker may have been planning on releasing them early on as he opened up the tunnel between Arkham East and West, presumably to spread them out and ultimately doom anyone stationed there as he did not care for them. This caused a couple of Joker's Henchmen to question the tunnel's opening before the lunatics were released.

The Lunatics seemed to embody the deservedly nightmarish reputation Arkham Asylum earned: the themes of insanity, depression, severe isolation and loneliness. Their very existence was an assault on all the senses, perhaps not evil, but certainly badly lost souls still capable of horrific acts as the pain in their minds pushed them to inflict this pain and even death on others. They were notably the only lethal obstacle besides electricity that could still harm Batman even after Joker's defeat.

Their appearances prior to incarceration in the Penitentiary were lost. Their appearances in the game were almost all uniform plus the remaining necessities of extreme high-security confinement that left them looking bald, hunched over and skinny with their insanity-driven strength compensating for their lack of physical bulk.

Before Arkham Asylum Incident
During his time at Arkham, Hugo Strange studied the inner workings of the brain. In order to do that however, he experimented on the more forgettable inmates. In order to cover up his operations the future lunatics were lobotomized, driven to madness, locked up and then forgotten, only receiving one small meal per week hence their skinniness. During his experiments on them Strange perfected Mad Hatter's  post hypnotic suggestion technique to later use on Quincy Sharp and TYGER. The lunatics that managed to escape either committed suicide at Dead Man's Point or found caves to live in.

Arkham Asylum Incident
After Batman found Sharp, Joker revealed to him through security footage that Harley Quinn released Poison Ivy from her cell. After expressing admiration for their antics, Joker released most of the lunatics from their containment units to attack Batman throughout the remainder of the incident. They were later assumed to have been placed back into their cells once Joker was defeated.

After Arkham Incident
Most of the surviving lunatics of the asylum were treated medically before being taken under the "care" of Strange to experiment on again. Several of them were later supplied to Penguin for his forces to use as target practice.

Arkham City Incident
While there were no signs of the lunatics inside Arkham City, a large number of dead ones (as well as other inmates) could be found hanging from the ceiling by their wrists at the main entrance to Wonder City.

As seen in the Arkham City Stories, the lunatics were failed experiments of Strange. It was rumored that he kidnapped the prisoners of Arkham City during profiling and experimented on them; those same stories said Strange's successful test subjects served as TYGER operatives while the unsuccessful inmates were subjected to the same procedure Strange used on the lunatics and left to roam the streets. It was also revealed that they were used by Strange to continue his experiments on mind-control in order to properly "influence" Sharp and he gave them to Penguin for target practice once he was done with them.

Gameplay
In Story Mode, lunatics were often found roaming aimlessly in the opens areas of Arkham Island muttering to themselves or performing various bizarre activities such as running around at nothing, trying to catch flies or scratching at the ground.

Once they spotted Batman, the Lunatics ran toward him while screaming, jumped onto his back to assault him, and ultimately tried to crush his ribs and lungs. The player could stop them from latching onto Batman by pressing the counter button, smashing them on the floor, or striking them to performing a Ground Takedown in order to disable them. If they were already on top of you, they could be thrown off by mashing the run button. That meant that this method could be used to throw them great distances of height, which shocked them and made them pass out.

Lunatics are the most resilient enemies in the series as a whole. Unlike other enemies mere strikes cannot finish them off. The only way to incapacitate them is to use a Ground Takedown or Ground Pound on downed lunatics, lure them into electrocuting themselves at electrified doorways while they're jumping at you or (only in Story Mode) make them fall from a great height. On the other hand, they are easier to knock down the ground with any counter (Freeflow Combat or not) and they cannot dodge the Batclaw. Note that Ground Pounds are slow, so it's advisable to time them properly.

Due to this resilience, lunatics are featured in the challenge map "Totally Insane". The number of lunatics makes it increasingly difficult to fight off the hordes of inmates and patients.

Trivia

 * The lunatics technically did not belong to any faction as they were completely insane.
 * They were the only enemy type that didn't make a return in any other title after their introduction. However, dead lunatics could be seen when Batman entered Wonder City and were alluded to in the City stories where it was rumored that Professor Strange had experimented on the lunatics and later provided them to Penguin as target practice, which was indirectly confirmed in an interview tape where Penguin mentions them as "dribbling monkeys".
 * Lunatics dressed like Batman could be seen during the third and final Scarecrow Nightmare.
 * Considering that the Character Trophy for the lunatics was present in Batman: Arkham City it was possible they were going to have a bigger role and larger presence in the story, but ultimately their appearance was scrapped save for the ones in Wonder City.
 * Many lunatics were able to withstand gunshots and only two were killed by Joker's Henchmen, one from being shot multiple times in Arkham North and another one lying dead in the area between Arkham North and East after being beaten by a group of Raincoat Henchmen.