Never say never. Already, the 21st century has brought any number of surprises when it comes to the DC properties that have appeared on screen: a “Suicide Squad” movie, an interconnected TV universe centered around Green Arrow and The Flash which has also introduced all the niche heroes of “Legends of Tomorrow” into the live action arena, another show that’s all about Bruce Wayne as a little kid. Warner Bros. seem game to try anything; even “Justice League” looks to be digging into the relatively-obscure (to mainstream audiences) “New Gods.”

RELATED: 15 Marvel Events You Will NEVER See On-Screen

With that in mind, you can sometimes say never. For all that the on-screen DC projects -- the Arrowverse on the small, the DC Extended Universe on the big -- are willing to take a roll of the dice on some wackier ideas, there are some concepts from the comics that defy adaptation. Whether it’s crossovers which are simply unfeasible, expensive or plain ill-advised, we run down the 15 DC events you will never see on-screen.

15 ROBIN WAR

Robin War cover

The Batman, played by Ben Affleck, introduced in “Batman V. Superman” is not a Caped Crusader who has sidekicks. He has returned to his original solitary nature, isolated from the rest of the world in his single-minded quest for justice. Inspired by Frank Miller’s iconic “Dark Knight Returns,” this is a grizzled, aged Batman who has been playing the vigilante game for years, with a significant history behind him: including, according to a bit of production design, a Robin apparently slain in the line of duty by The Joker.

In the comics, Batman has not only persevered with the sidekick thing, but he’s been the mentor for multiple Robins. Sometimes, there are multiple Robins at the same time, as in the recent “We Are Robin” series depicting a vigilante youth movement who claim the mantle for themselves. The movement lacked the approval of any of the old Robins -- Damian Wayne, Dick Grayson, Jason Todd, or Tim Drake -- or the Gotham City police. Thus they erupted into the “Robin War” crossover, something not possible in a movie world where the only Robin is six feet under.

14 OUR WORLDS AT WAR

Superman Our Worlds At War Imperix by Ed McGuiness

For whatever reason, it doesn’t appear that the DCEU is going to be an iteration of the DC Universe that places Superman at the center. Despite “Man of Steel” introducing the new fictional universe, the character was killed off during his fight with Batman in “Dawn of Justice,” and on the TV side of things he makes either cameo appearances in “Supergirl,” or will presumably be referenced off-screen or turn up on screen as a baby in the forthcoming “Krypton” prequel show.

That probably means the majority of “Superman”-related events from the comics are off the table, in terms of source material  for his on-screen incarnation. That's a shame, since there’s a rich vein to be tapped there! The “Our Worlds At War” crossover, from the underrated early ‘00s era of the Man of Steel’s series, has some serious blockbuster potential. The world’s heroes join together to stop Imperiex, a cosmic force who has realized the universe is imperfect and is trying to “hollow” it out -- beginning with Earth.

13 DC ONE MILLION

The Justice Legion A travelling back in time

Grant Morrison fans ought to make their peace with the fact that the mad Scot of comics is unlikely to see any of his strange, superlative works adapted to the big screen. Movie versions of everything from “The Invisibles” to “Seaguy” have been developed over the years, with little to show for it. It seems as if elements of his early “JLA” run might figure into the upcoming “Justice League” movie, but there’s no chance that the films will follow those comics to their end point.

“DC One Million” was a crossover event by Morrison and artist Val Semeiks, following on from “JLA” and presenting a far-off possible future where the League is still in operation (after a fashion). The Superman of the 853rd century is a descendant of Kal-El, and the entire solar system is policed by a new Wonder Woman, Hourman, Starman, Aquaman, The Flash and Batman inspired by their predecessors. It would be pretty radical for the DCEU to sack off existing continuity in favor of a speculative story for anything further than the flash-forwards from “Dawn of Justice.”

12 NO MAN'S LAND

All comic book crossovers involve some kind of lead-in. Conflicts which have been simmering for a while suddenly boil over. Other times, there are literal storylines building up to an overarching event. Then there are the rare storylines like “No Man’s Land,” which entirely shook the status quo for the “Batman” family of comics for almost a year. We mean that literally. It involved an earthquake tearing Gotham City apart, the US government abandoning the disaster zone, and the Dark Knight struggling to impose a sense of order during a state of emergency.

It’s not always perfect in execution, but the concept is flawless. Part of the fun is how far-reaching the consequences of a ravaged Gotham are. All the various Bat-related comics tie into it, Lex Luthor shows up to fund the “reconstruction” of the city, and the Caped Crusader turns his back on the “Justice League” for being largely absent during the cataclysm. Unless Warner Bros. commit to a similar interconnected set of stories, or possibly a TV miniseries, don’t expect to see “No Man’s Land” on screen.

11 FOREVER EVIL

“Gotham” is the Batman show which gets that the Dark Knight isn’t the only thing his city has going for it. There’s also his extensive, colorful rogues gallery, which is somewhat under-served in TV and movies which continually return to the Joker/Riddler/Two-Face well. It may be telling the origin story of Kid Bruce, but in “Gotham,” the villains rule. So, really, there’s no reason for “Forever Evil” -- a recent DC crossover where the bad guys win -- to be adapted for live action.

It also involves a heck of a lot of deep dives into the history of the DC multiverse, featuring as it does the Crime Syndicate, an evil version of the Justice League from an alternate reality. Considering we’ve yet to establish the “Justice League” on screen, introducing an evil, inverted version would make no sense; neither would a movie where Jesse Eisenberg’s Lex Luthor leads a team of his fellow mainline continuity villains against the forces of the Crime Syndicate.

10 WHATEVER HAPPENED TO THE MAN OF TOMORROW?

Whatever Happened Man of Tomorrow

One of Alan Moore’s first great works of revisionist superhero comics, with gorgeous Curt Swan pencils inked by the equally legendary George Pérez and Kurt Schaffenberger, “Whatever Happened to the Man of Tomorrow?” was intended to close the book on the Silver Age conception of Superman, and bring forth the brave new mulleted, yuppie version of Kal-El introduced in John Byrne’s “Man of Steel.” Silver Age Superman was one who went on broad, sci-fi tinged adventures, full of wit and wackiness and a plethora of supporting characters and enemies.

It’s a monumental work, with a great deal of its power lying in context: this was a decidedly dark spin on light source material, the closing of a book that juxtaposed violent reality with the superhero escapism of the Silver Age. You won’t see this story on either small or big screen; Kal-El is dead in the movies, as of the end of “Batman V. Superman: Dawn of Justice,” and the Snyderverse is already dark enough as is. The inversion would be a radical adaptation of the story that brought some Silver Age innocence to violent reality.

9 ARMAGEDDON 2001

Armageddon 2001 1 cover by Dan Jurgens and Terry Austin

Crossovers take months, even years of planning. These days, the Big Two have to plan their big publishing events around a constellation of interconnected titles who have to be factored into the overarching plot, as well as taking into account marketing pushes and movie tie-ins. That requires a lot of secrecy, too, since the long lead-in periods give the potential for leaks. With NDAs and the like, they’re primed for that now. In 1991, DC were less prepared.

“Armageddon 2001” is infamous among comics fans for being nigh incomprehensible. A mysterious character, previously a superhero who became a totalitarian despot, rules over a future dystopia; a young rebel called Ryder travels back in time to kill this hero before they can make their heel turn. Captain Atom was clearly being set up to be this despot, only for that twist to be leaked ahead of time. So, DC quickly changed tack, messed the whole thing up, and botched the entire story in the process. Not the most prestigious story to bring to the screen.

8 KNIGHTFALL

Azrael Batman Knightfall

Chances are, the closest we’ll ever come to a non-Bruce Wayne Batman in live action was Joseph Gordon Levitt’s orphaned cop John Blake being entrusted with the Batcave at the end of “The Dark Knight Rises.” Bruce has held onto his cowl for the most part in the comics, too, but there have been times when -- for a variety of reasons -- he has had to relinquish the mantle to a young upstart. Former Robin Dick Grayson took over when he came unstuck in time, various futures have predicted protegees taking over for him, and then there’s “Knightfall.”

The first part of that comic storyline has already appeared on screen -- Bane’s breaking of Batman’s spine in the aforementioned “Rises” -- but the rest? Fat chance. During a period of convalescence after his shattered back, Bruce allowed apprentice vigilante Azrael to take over as the Caped Crusader for a spell. It shook things up a bit, as was the intention, but don’t expect audiences to pay for a ticket to a Ben Affleck movie only for him to be relegated to a sidekick gig as someone else leaps around in the tights.

7 JLAPE

JLApe Gorilla Warfare cover by Art Adams

One of the greatest successes of the CW’s “Flash” series so far has been getting Gorilla Grodd into a live-action setting. The genius, vociferous and supervillainous ape is one of the stranger members of Barry Allen’s comic book rogues gallery, so it’s a credit to the showmakers that they nailed the special effects that brought the character to life, and made his appearance in that world credible. With all that said: there is no way “JLApe” will ever make the same transition.

The common denominator being that the crossover event, punnily subtitled “Gorilla Warfare,” involved the ape denizens of Gorilla City attacking the human world by releasing experimental bombs. They are experimental because they turn people into gorillas... including the Justice League. So Batman, Wonder Woman, Superman, The Flash all become ape-people. Green Lantern quotes the “It’s a mad house!” speech from “Planet of the Apes.” It’s not one of the better “JLA” events, and unless the DCEU gets way more goofy, it’s not appearing on screen.

6 RANN-THANAGAR WAR

Hawkgirl Hawkman and Adam Strange in Hawkman 47 by Chris Batista

The failure of the “John Carter” movie has basically poisoned the well for all hapless-dorks-teleported-beyond-space movies to come in the near-future. That's a real shame, because “Adam Strange” -- a comic with essentially the same premise, starring an Earth man who is teleported to the planet Rann and becomes its jetpack-and-raygun-wielding champion -- is great. At least Hawkman is getting his day, as a part of the “Legends of Tomorrow” series.

Carter Hall’s various, confusing origin stories tend to involve a similar fish-out-of-water premise. It made a kind of sense when their worlds almost literally collided in comic book event the “Rann–Thanagar War.” “Rogue One” shifted the goalposts when it comes to the sort of stories that can be folded into genre movies, bringing the classic war movie narrative into the world of “Star Wars,” but it’s doubtful conflict on that cosmic scale could happen in the DCEU without significant build up.

5 BLACKEST NIGHT

“Green Lantern” hasn’t been particularly well-served by the live action arena thus far. The Ryan Reynolds-starring film has been reduced to a punchline in the actor’s far more successful, far more popular “Deadpool” superhero movie, and attempts to get a new adaptation off the ground as part of the DCEU -- with the concept apparently leaning more heavily into the “cops in space” procedural angle -- don’t seem to be moving with much haste. That means you shouldn’t hold your breath for a “Blackest Night” movie.

On-screen continuity isn’t the only reason. It’s a surprisingly bleak, violent event, with a cosmic personification of death reanimating scores of dead superheroes in pursuit of his goal of eliminating all life from the universe. It would be a surprise, and also incredibly ballsy, if Warner Bros. decided to make what is essentially a superhero zombie movie -- well, “The Walking Dead” is pretty popular. If they did, though, they could aim for that R-rating “Deadpool” and “Logan” have legitimized for the comic book movie. It’s also incredibly unlikely.

4 CRISIS ON INFINITE EARTHS

Crisis on infinite earths

The most iconic of DC events, “Crisis on Infinite Earths” has long since outgrown its humble beginnings. When it was first being published, the intention was for the Marv Wolfman and George Pérez miniseries to tidy up what had become a particularly messy continuity over 50 years of publishing. The world of DC was cluttered with alternate universes, multiple iterations of the same character, and a lot of inconsistency in portrayals of heroes, villains and story arcs alike.

“Crisis,” then, is mainly housekeeping. Unless the DCEU or TV universe get comparably convoluted, there’s no need for an adaptation. More than that, the comic gets pretty abstract in places -- even more out-there than Marvel’s recent “Doctor Strange” movie -- as alternate realities collapse in on each other, universal beings try to impose their will on proceedings, and The Flash sacrifices himself within the ill-defined “Speed Force” in one of the most iconic denouements in comics...which probably wouldn’t work nearly as well in literal motion.

3 52

52 Week One cover

In an ideal world, “52” would be the greatest superhero TV series ever made. The groundbreaking experiment in comics publishing which paid off, and then some, the weekly series utilized a television-style rotating writer’s room to pen a series that tied together a multitude of plots involving C-list characters -- most of the heaviest hitters were out of commission, allowing for some of the stranger, more colorful cast members from the DC universe to step up for a truly fresh, thrilling bunch of adventures.

It was inspired by serialized television but, ironically, would be essentially impossible to pull of as serialized television. “52” travels around the world and across the universe. It involves a cast of thousands, most of them with some form of super-power, which takes time and money to put on the screen. It also stars a whole bunch of niche characters audiences wouldn’t necessarily be willing to tune into -- certainly not in enough numbers to justify the kind of price tag an adaptation of “52” would necessitate. Sadly, we do not live in this ideal world.

2 IDENTITY CRISIS

DC's Identity Crisis raped and killed Sue Dibny, Elongated Man's wife

Rags Morales and Brad Meltzer’s “Identity Crisis” was a cause célèbre when it was initially being published. Its lasting legacy has been a wholly negative one for the same reasons it was a must-read as it was coming out, telling as it did a lurid, exploitative and nasty tale of rape, murder and memory-erasure. It opened with the unnecessarily graphic murder of Sue Dibney, crime-solving wife of stretchy superhero Ralph -- better known as the Elongated Man -- in what eventually proved to be an ill-judged attempt to bring grim reality to bear on the colorful world of superheroes, a trope which has obsessed comics creators ever since “Watchmen.”

There’s a rumored pivot to come in the DCEU, where the darker tone Zack Snyder has set in “Man of Steel” and “Batman V. Superman” will brighten in his forthcoming “Justice League.” Otherwise, “Identity Crisis” might have fit perfectly into the violent, nihilistic superhero world where “Suicide Squad” takes place. As it is, the story would not work on the big screen -- unless Warner Bros get so desperate for IP to exploit that they make an Elongated Man film -- nor on the CW’s shiny happy world, where standards and practices would surely balk at a prime time superhero series featuring so much objectionable content.

1 JLA/AVENGERS

The Justice League and Avengers meet in JLA/Avengers by Marvel/DC Comics

Well, obviously. It’s already been shown what an uphill struggle it’s been for Marvel Entertainment to work with the various film companies who still hold licenses to properties it sold the movies rights to during their period of ‘90s bankruptcy; Sony only gave up “Spider-Man” when it became clear they had no idea what they were doing with the franchise, yet Fox still hold a tight grasp upon “Fantastic Four” and the “X-Men.” Can you possibly imagine a world where Disney and Warner Bros. can play nice long enough to allow completely separate fictional worlds to collide?

There have been a surprising number of inter-company crossovers over the years -- even before 1996’s blockbuster “DC vs. Marvel” miniseries, Spider-Man had crossed paths with Superman and Batman had teamed up with Daredevil. However, the holy grail was always Kurt Busiek and George Pérez’s “JLA/Avengers,” a book which had first been mooted all the way back in 1978, but only became a tangible reality in 2003. It took that long for the two companies to come to a suitable arrangement when publishing a four issue limited series. Can you imagine the decades, nay, centuries needed to balance both the business concerns, let alone egos, of those involved with a movie crossover?

Any other "unadaptable" crossovers unlikely to get the live-action treatment? Or do you think some of these stories could work in the DCEU? Sound off in the comments below!