The run opened with a Flash Forward with Gotham Girl declaring that Batman would die. At the end of the run, Bruce was still alive, so unless she was talking about the Detective Comics #1027 story "Legacy" (which had Bruce contracting and dying from cancer after saving Doctor Phosphorus as an old man, but with no appearance from Gotham Girl) or the Thomas Wayne from the Flashpoint timeline, whose fate was ambiguous at the end (though he was ultimately revealed to have survived), what was she talking about?
Said opening also has Gotham Girl say she and Duke Thomas end up married — yet there were no hints of a romance between the two throughout the entire run, and Duke barely appears after the third arc and certainly not with her.
Chuck Dixon's Batman and the Outsiders run set up the deceased Ralph and Sue Dibny as a pair of ghost detectives who would act as recurring allies to the team. This was nixed very early on, leading to the Dibnys making only sporadic cameos across the DCU until Flashpoint rebooted everything. There was also the matter of an underground club where teens were granted a chance to receive superpowers from one of the surviving Bloodlines parasites. This too went nowhere.
From 1995-98, writer Doug Moench and artist Kelley Jones were in charge of the main Batman title. During their first three years on the book, a nameless puppeteer holding a Batman puppet appeared in the background of many stories. He would be there when Batman was solving a case or when he was throwing a party as Bruce Wayne, but he never let his presence be known. The idea was that in the fourth year of their run, which they knew would be their last, they would properly introduce the character as someone who knew Bruce's identity, was capable of manipulating both Bruce and Batman and has been preparing to confront Bats on his own terms, but this was never followed through. Jones later explained in interviews that editorial demanded that in their last year they tied the book with the other bat-titles where they had been allowed to ignore them and just tell their own self-contained stories before. This threw a wrench on the puppeteer arc and some other stories they were planning, including one with Poison Ivy.
Brian K. Vaughan wrote a Batman one-shot where he introduced a mysterious new villain called the Skeleton, who was running around impersonating other Batman foes to cover his tracks. The hope was that Vaughan would become a regular writer on one of the Batman books so that he could make the Skeleton into powerful new player in the franchise, but obviously, this never occurred.
In the DC Year of the Villain one-shot The Riddler, Apex Lex convinces Nygma that the flaw in his plans is simply being the Riddler in the first place, and that if he could abandon this, in the same way as Lex abandoned his obsession with Superman, he'd be able to decide who he really wanted to be. It's not clear if writer Mark Russell was going anywhere with this, but a few months later, Riddler appears in Batman (Tom King), more obsessed than ever, and just says that didn't work.
For a few years Black Mask was not Roman Sionis (who was killed by Catwoman in retaliation to what he did to her sister) ,but a Brainwashed and Crazy Jeremiah Arkham. During the New 52 however this was undone...but not via a cosmic retcon since there is dialogue in Court of Owls that still indicates his time as Black Mask still happened, but was resolved off panel and the DC Comics website only vaguely mentions Jeremiah taking on the mantle during Dick Grayson's time as Batman, which is accurate but still doesn't address how it was reversed. Verges into both Fridge Horror and Fridge Logic when you consider how there were basically no consequences for any of the people he killed.
Batman: The Widening Gyre saw the Hero Killer Onomatopoeia slowly work his way into Batman's confidence by taking on a new persona as "Baphomet" and slowly winning the Dark Knight's trust. Eventually, Batman comes to see him as a true hero and companion, taking him to the Batcave where his lover Silver St. Cloud was. By then, "Baphomet" reveals himself as Onomatopoeia and slits Silver's throat in front of a horrified Batman, ending the story on a massive cliffhanger. Since then, the audience has been left hanging because there have been no followups or sequels to this story.
Devin Grayson's run on Nightwing's ongoing was greatly cut into by several different events, including Infinite Crisis, thus preventing her from finishing the story she intended.
The New 52 series' last arc had Dick moving to Boston and finally getting an established supporting cast, including his roommates, one of whom worked for the mayor and had a bone to pick with superheroes, especially Nightwing. At the same time, a girl that Dick was babysitting learned that he was Nightwing, and eventually Dick is forced to save her when she steals his gear and tries to avenge her parents. Dick also reconciled with Sonya Zucco, the daughter of his parents' killer, Tony Zucco. All of this was thrown out when Dick was outed in Forever Evil and never mentioned again.
It was heavily implied at one point that Alfred was falling for Tim's stepmother, Dana. Then Blüdhaven blew up and Dana was never seen again.
Red Robin was clearly developing a major villain who had been working behind the scenes and was never able to be named on panel before Flashpoint happened. Prior to this the Ünternet arc was cut short of its intended length and had its consequences watered down by executives.
Julie Madison, Bruce's steady girlfriend in the film, was originally scripted to have a more prominent role where Poison Ivy actually killed her and motivated Bruce for revenge. This was cut by the time of filming, but the movie clearly still has elements of this in the screenplay and Julie abruptly vanishes from the film in the third act without even so much as a reference as to where she is.
In 2017, the late Coolio revealed that his "Banker" character was actually supposed to be the Scarecrow, who was supposed to have been the villain of a fifth film — which didn't happen due to the disappointment that film caused, which eventually led to the series being rebooted into The Dark Knight Trilogy.
Subverted for the Wayne Killer arc; it essentially disappears after the first half of Season 1, but returns in full force midway through Season 2.
Also during Season 1, the importance of the Arkham deal goes nowhere. Possibly also averted, since the second half of Season 2 focuses heavily on what the corrupt elements in Gotham are doing with Arkham.
Late in Season 1, the corrupt members of Wayne Enterprises seem to have something sinister planned for Bruce, given Reggie Payne's line "Now's the time to make a move on the kid." This may be simply misdirection, since what they have planned seems to be merely Bunderslaw telling Bruce the truth about Wayne Enterprises and how powerless he is to stop it.
Then its revealed near the end of Season 3, these arcs are revealed to be connected and resolved for the most part by the end of the season.
Lee was revealed to be pregnant in the mid-finale of Season 2, many fans were hoping for baby Barbara (aka the future Batgirl), but sadly the baby was miscarried. Then Barbara and Jim have a one night stand in Season 5 that results in her ending up with a One-Night-Stand Pregnancy, the baby named Barbara Lee Gordon and raised by her mother, father, and step-mother (Lee Thompkins).
The fifth season was hit hard by this due to the reduced season; the season 4 finale and 5 premire hinted that past characters including Freeze, Firefly, and Scarecrow were going to be amongst the main threats along with new enemies including Man-Bat. None of these characters ever play a key part beyond a mention and the latter doesn't even appear again after season 4.
Western Animation
Due to being Screwed by the Network, Batman: The Brave and the Bold had to abort the Shards of Equinox arc, an arc that would have focused on finding the various personality shards of Equinox that were scattered through the universe. The Grand Finale episode even made a Lampshade Hanging over the cancellation of the show by being about getting the show canceled.
in interviews