Skeletons

"HAHAHA! Your in my world now, little bat."

- Scarecrow about how his henchmen can kill Batman now.

Skeletons are a unique type of enemy found in Batman: Arkham Asylum. They appear as greyish human Skeletons with an ominous green or red glow emanating from their bodies. They are only encountered in the Scarecrow Nightmare levels. There are two variants: Normal and Titan-enhanced. Titan enhanced Skeletons behave much like the Titan Henchman, except for that they crumble instantly upon hitting a wall. When a Skeleton is hit, it makes a slight cracking noise and when defeated, it crumbles (or shatters) to a pile of bones.

Arkham Asylum
In Batman: Arkham Asylum, Scarecrow had some of Joker's henchmen come to work for him. In the fear toxin, Batman mistook them for Skeletons. The gas wasn't effecting them though. They were in the second and final dream. They were not in the first one so they could surprise Batman later in the game when he opened the doors to save Gordon. They helped him fight against Batman, but were taken down much easier and failed at the succession of killing Batman.

Arkham Knight
As Batman drove around the toxin covered city, on three occasions he was haunted by a giant version of Scarecrow, whom would summon Titan Skeletons to fight for him as part of the hallucination.

Scarecrow's Nightmare Challenge Map
They were the only enemies in this challenge map.

Weapons
Swords: Despite their appearance, they are the equivalent to pipes.

Torches: Their equivalent of Stun Batons.

Glowing Knifes: Skeletons that use them are equivalent to the High Security henchman and glow red instead of green.

Superhuman strength: The titan skeletons fought like actual titans except far more fragile.

Trivia

 * While it is implied that the skeletons are actually inmates only seen through the hallucinations, it doesn't explain how they go down much easier than real inmates. It could be that the fear toxin actually makes the user stronger, or it could be that Batman saves no punches when he thinks they are aren't alive/real.
 * Interestingly however, a Titan Skeleton goes down simply from colliding to a wall, while an actual titan henchman requires this to happen multiple times, in addition to repeated punches. This was possibly because it would take longer to fight several Titans of normal health.