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Nightmare Fuel: Death Of The Family
Every time the Joker appears in Death Of The Family is Nightmare Fuel. A number of readers have never found Joker to be particularly haunting, but this storyline has changed that.
For starters, Commissioner Gordon is at the police station with his fellow officers and they are just going about their usual business. Then Joker comes in. First he turns off the lights. Gordon is trying to protect himself and he can't see anything. He can hear Joker reciting bad jokes. Just when it looks like it's all over, Batman comes in and turns the lights back on. Gordon is alive, and surrounded by dead cops. He also finds out that Joker has taken his face-skin back. Later, it's stated that 19 police officers were killed by Joker. It's not said how many officers make up the Gotham City Police Department, but that's still a lot.
As the event progresses, across all the books, Joker's flesh decays considerably. By Batman 16, there are flies buzzing around his face, and he doesn't seem to care.
Two Words:Batfamily Clowns. In the finale, seeing the Batfamily turn into Joker versions of themselves and try to kill each other is screwed up.
One of the scariest things about the Joker in this story is how he recreates his original crimes but changes details about them that throws everyone off, including Batman.
One of the scariest things is that, on some level, Joker knows who everyone in the Batfamily, and many of those allied with them, are. Maybe he can't actually accept them without the masks, but we'll never really know whether or not it played a part in what the Joker did to the Gordons in the Killing Joke; or to Jason. And the not knowing means they'll never be safe from this version.
Batman counters this by threatening to reveal his real name from before he was the Joker. Judging by the Joker's reaction, this is what scares him the most.
Unrelated to the main plot, but in Batman #13, Harvey Bullock mentions the birth of a two-headed lion cub, with a lot of children there to see the birth of a new lion cub in general, and seeing... that.
Damian: I think there's something wrong with it. Dick:You think?
The journey into Arkham Asylum as the main story marches toward the climax; Joker had taken over the entire facility and made it seem like it was operating as usual under threat of murdering the families of the security staff. Those without families were imprisoned and made to dress as Batman and the Joker and dance for days on end. The Joker has also had the Dollmaker create a tapestry of his various encounters with Batman on the bodies of various inmates who are all still alive. The Batman then encounters a horse on fire, has to fight off a horde of inmates in riot gear, go through various elements of his rogues gallery, and come face to face with the Joker who has dressed up a set of the guards as the Justice League in a twisted reenactment of Arthur having to withdraw the sword from the stone - the point being that none of them - the heroes - are as good as Batman, the mock-up designed to electrocute them immediately. Batman himself is then electrocuted into unconsciousness, having no choice but to go along with the Joker's twisted demands. And we have no idea if the Arkham staff survive once the Joker leaves for the Batcave.