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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 becomes increasingly rotten. 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. Judging by the Joker's reaction this is what scares him the most.