"Batman: Death in the Family" was a reader based decision. Jason Todd ,aka Robin,'s life was put in the hands of the readers. Let Robin live, or have the Joker kill him. The character was killed off by a vote of 5,343 to 5,271. And so the Joker beat Robin nearly to death with a crowbar in an abandoned factory. He placed a bomb inside and left, seeing if Batman could rescue him in time. The explosion killed Robin and filled Batman with a loss so great that he would never forgive himself for not being able to save Todd. The grief and sadness he felt was comparable to the death of his parents.
In "Joker's 5 Way Revenge" the Joker goes about tracking down and killing the former members of his gang. By the end of the story he manages to blindside Batman. He has his on the ground at his mercy, his foot on Bruce Wayne's throat. Right then and there he could have killed Batman and ended one of the world's most famous and heroic Heroes. Instead, he walks away just so that he can kill him later down the road once he finds a way to "destroy him properly."
In "No Mans Land" the Joker kidnaps dozens of babies and keeps them locked up in the basement of the Gotham's police station. Commissioner Gordon's second wife, Essen Gordon tracks the Joker down and confronts him. With her pistol and aimed at him the Joker literally throws a baby at her forcing her to drop her gun and catch the infant.
After she saves the child the Joker shoots her in the head. The babies then crawl around on her lifeless body. One even sits calmly in a pool of her own blood. I can't put into words how fucked up that is. The Joker then surrenders to the other police officers who arrive shortly thereafter.
In "Batman Confidential #11" the Joker creates a blimp which explodes over Gotham city. The exploding blimp rains down poison glass on the people below. Yes, POISON GLASS, which forces the innocent people's faces into a twisted smile mimicking the Joker's, as they die. This attack kills "a Significant portion of Gotham."
It should be noted that during the "Golden Age" the Joker is most remembered for being a serial killer.
In "Death of the Family" the Joker escapes from Arkham Asylum and leaves behind his own face, nailed to the wall as a sign of his "rebirth". One year later recovers his face which had been preserved at Gotham Police Department, killing 19 police officers in the process. He reattaches his face and kidnaps the entire Batman family, Nightwing, Robin, Red Hood, Batgirl, and Red Robin and ties them up in the batcave. He sets them at a dinner table with their faces bandaged. The joker forces batman to take a seat at the head of the table which is actually an electric chair. A brainwashed Alfred serves Batman a stew which appears to be made from the faces of his family at the table.
Batman later frees himself and The Joker escapes. Upon freeing the others Batman realizes that The Joker didn't actually remove their faces and was just fucking with his head.
After which he threw the body on stage.
The animated movie Dark Knight Returns has one of the most unexpected fight scenes of any Batman movie. Batman chases the Joker through an amusement park, as he has before. However this one is full of people which the Joker is indiscriminately killing. In the video posted above the Joker kills 13 people in less than 30 seconds while running through the park. Also he has a fucking Batarang in his right eye socket during the entire video.
Batman finally corners the Joker in the Tunnel of Love ride and proceeds fight the Joker. The Joker stabs him several times but Batman, uses his hand to hand combat skills, both disarming and severely injuring his neck as Batman expresses the guilt he feels for all the people the Joker has killed. He blames himself for allowing the Joker to kill so many. This is where the Joker has won. Batman is consumed by rage and guilt. The Joker begins laughing hysterically and says, "I win. I made you lose control. And they'll kill you for it." He breaks his own fucking neck to frame Batman for his own death.
"The Killing Joke" has one of the most ambiguous endings of any Batman comic or graphic novel. Pictured above is the final panel. Batman managed to rescue Commisioner Gordon who failed to be driven to madness even with the Joker's extreme efforts. Batman then proceeds to chase the Joker through the amusement park while the Joker tells him a joke that he suddenly remembers.
"Y’know, it’s funnyâ€¦this situation. It reminds me of a jokeâ€¦[pauses] See, there were these two guys in a lunatic asylumâ€¦and one night, one night they decide they don’t like living in an asylum any more. They decide they’re going to escape! So, like, they get up onto the roof, and there, just across the narrow gap, they see the rooftops of the town, stretching away in the moonlightâ€¦Now, the first guy, he jumps right across with no problem. But his friend, his friend daredn’t make the leap. Y’seeâ€¦y’see, he’s afraid of falling. So then, the first guy has an ideaâ€¦He says â€œHey! I have my flashlight with me! I’ll shine it across the gap between the buildings. You can walk along the beam and join me!â€ B-but the second guy just shakes his head. He suh-saysâ€¦He says â€œwh-what do you think I am? CRAZY? You’d turn it off when I was half way across!â€ Ha Ha Ha Ha Ha! Ha Ha Ha Ha Ha Ha Haaâ€¦Fnff oh, do excuse meâ€¦Ha Ha Ha Ha Ha!
After the Joker tells this joke the story ends with both him and Batman laughing, maniacally. It seems as though the Joker was able to prove his point by driving Batman insane by giving him "one bad day."
In "Injustice" the Joker breaks the spirit of Superman. He starts by killing Jimmy Olsen, a close friend and coworker of Superman's alter ego Clark Kent. The Joker then kidnaps Lois Lane and performs open heart surgery on her while in a submarine with Harley Quinn. Superman tracks them down and tears open the submarine finding Lois Lane on an operating table while The Joker and Harley attach a Heart Monitor to Lois' heart. Catching Superman off guard the Joker gases superman with a mixture of the Scarecrow's Fear poison and Kryptonite.
The Joker's gas tricks Superman into believing that his pregnant wife Lois Lane is the nearly unstoppable villain Doomsday. Superman grabs "Doomsday" and flies him into space killing him from lack of oxygen. Only then does the gas wear off and Superman realizes he has killed his wife and unborn child. When Lois' heart stops it triggers her heart monitor which detonates a Nuclear Warhead destroying Metropolis and killing the citizens Superman had spent years protecting.
Read more: http://imgur.com/gallery/q0f38