While Crisis on Infinite Earths is already confirmed to involve a ton of characters from different DC media continuities, there is an equally large amount of worlds that haven't been confirmed to be revisited in the crossover.
Many of these have been heavily speculated to get a surprise inclusion, some are pretty much longshots, but others are all but confirmed. Here's a list of the various DC shows and movies that have yet to be officially confirmed but could make some sort of appearance in The CW's ambitious Arrowverse crossover.
It might seem a bit ridiculous, but given how well-loved DC's various animated productions have been throughout the years, Crisis would be doing fans a disservice out if it didn't include them in some way.
The most obvious candidate from these animated series' would be the world of the DC Animated Universe (DCAU) kicked off in the modern age by the critically acclaimed, Batman: The Animated Series. Other animated continuities include DC's current animated movie universe, as well as the universe of Young Justice.
These cartoon worlds will already have some form of representation in Crisis. Kevin Conroy, who voiced Bruce Wayne/Batman in the DC Animated Universe, is playing the character for the first time in live-action in the television event. Given his aged status, this may actually be the old Bruce Wayne from Batman Beyond. It's a shame Michael Rosenbaum turned down his role in the crossover as he could have complimented Conroy as a live-action DCAU Wally West, a character he played in the Justice League and Justice League: Unlimited animated series.
The crossover will already supposedly involve Tim Burton's Batman in some capacity, but there are a wealth of other DC movies to pull from. The most notable would be the current DC Extended Universe, which had its latest entry this year with Shazam!. Given both the tumultuous status of that continuity, not to mention the cost of using any of the big actors, this is unlikely to be an option, however, as would any and all references to the recent Joker.
Another popular DC movie universe would be that of Christopher Nolan's The Dark Knight trilogy. It'd definitely be funny at the very least to involve those movies' realistic, grounded take on Batman, all in the midst of an interdimensional Crisis.
There are also older standalone movies such as Catwoman, Green Lantern, Steel and Jonah Hex, but their infamously poor receptions suggests it's better to keep them safely away from the crossover. The Arrowverse's version of Jonah Hex, who first appeared in Legends of Tomorrow, will be appearing in the event, though.
What about greater representation of the big three in the DCU: Superman, Batman and Wonder Woman?
The most obvious MIA DC television property in the event is that of Lois and Clark: The New Adventures of Superman. The first modern television version of the Man of Steel would fit right in with the Arrowverse characters, and would have three other Supermen to tag along with. Also absent is the George Reeves-fronted, Adventures of Superman series from the 1950s, which could bring the novelty of featuring a Superman in a black and white color scheme to the crossover. Sticking with the Super-family, there's also the 1980s Superboy series and, if anything, having a version of Superboy in the crossover event would also match the Crisis on Infinite Earths comic book more closely.
As for the Dark Knight: Burt Ward, the actor who played Dick Grayson/Robin in the 1960s Batman TV series, is confirmed for Crisis, but his role is still unknown. If he isn't portraying an adult version of his iconic role, than that particular TV world would be left open to being revisited in some other capacity. Fox's Gotham is also unrepresented, but given it that it was a far more recent series, and on a different network, any actors reprising roles from the show would be unlikely.
Lynda Carter is rumored to be appearing in the crossover, which would see her returning to her famous role as Wonder Woman from the 1970s TV series. Other TV incarnations of the Amazon Princess that could appear are much, much less likely candidates. The first of these is the Cathy Lee Crosby Wonder Woman, who only appeared in a made for TV movie intended to serve as a pilot for a potential series. This blonde version of the character was powerless, wore a strange '70s jumpsuit loosely based off of her costume, and bore more resemblance to the controversial, powerless mod-era Wonder Woman.
Another possibility is the Wonder Woman from NBC pilot that never made it to a full series order. While these characters are unlikely to show up, especially with Carter's version possibly in the mix anyway, their visual differences from her would be a nice contrast to see on the screen.
TITANS & THE DC TV-VERSE
It's been a back and forth as to whether or not the heroes from the DC Universe series, Titans will appear. They would definitely have some overlap with the Arrowverse versions of Deathstroke and Batman-related characters, making them feel more at home. The biggest issue with including the characters, of course, is giving their possible inclusion enough time to feel worthwhile, if not organic. If any characters from Titans appear, then cast members from Swamp Thing and Doom Patrol could also possibly be involved, too.
One particularly low point in superhero television was the 1997 Justice League of America TV pilot. This low budget, loathsome effort, described derisively as "Friends with superpowers," was also the first live-action appearance of Martian Manhunter. It'd be funny to see at least one of those versions show up, if only to prove how much better superhero shows have gotten in the last two decades.
Another prominent DC hero who has had no real representation in the Arrowverse so far is Captain Marvel/Shazam, and using the version of the character from the 1974 Shazam! series would be an easy way to do it without treading on the toes of the big screen iteration. An easy gag could even involve the heroes of the Arrowverse thinking that he's his Earth's version of The Flash. The Shazam! series also introduced the heroine Isis, and a version of this character exists on Legends of Tomorrow.
The only other possible DC-based show to pull from would be from Fox's 2010 Human Target series, which was canceled after two seasons. Without the name recognition of DC's roster of superheroes, though, it probably isn't well remembered enough to be worth sucking into Crisis.
For now, Arrowverse fans will just have to keep counting down the days until Crisis begins to see what notable inclusions and omissions will be in store.
Crisis on Infinite Earths begins Sunday, December 8 at 8 pm ET/PT on Supergirl, then continues in Batwoman on Monday, December 8 at 8 pm ET/PT and in The Flash on Tuesday, December 10 at 8 pm ET/PT. After the winter hiatus, the crossover will conclude on Tuesday, January 14 in Arrow at 8 pm ET/PT and in DC's Legends of Tomorrow at 9 pm ET/PT.