With all the discussion about the identity of Mr. Oz - and whether he's helping Dr. Manhattan attack the DCU, or preventing him somehow - one of the biggest clues is his collection of various DC characters within the walls of his mysterious prison.
That prison has played a role in everything from "Superman Reborn" to the events of Detective Comics, and its prisoners are sure to be central to DC Chief Creative Officer/President Geoff Johns' promised clash between Dr. Manhattan and the DCU coming to a head with Doomsday Clock.
In Detective Comics #940, readers were shown that Mr. Oz has more than one prisoner — two shapes were shown trapped in the cells, although their faces were not shown. Tom King confirmed to Newsarama that the shapes represent two mystery characters in those cells.
And of course, there's also the mysterious prisoner that Mr. Oz was speaking to in his earliest Superman appearance before "Rebirth" even began. In Superman #34 during the New 52, Mr. Oz also talked to someone he appears to have imprisoned behind a pair of doors. "If I let you out, I'm sure you'd offer an opinion," he says. Who was trapped behind the doors?
But who are the prisoners? How many of them do we know, and how many are unknown? And who else could be within the prison?
Prisoners We Know
As we try to figure out the identity of the mystery inmates, let's review first who we know was definitely imprisoned by Oz:
The imp is no longer a prisoner - having escaped - but he was once housed within one of Oz's cells. In "Superman Reborn," Oz said he took Mxyzptlk "off the table" as a precautionary measure. "It's not for what you have done, but for what you might do," Oz said. "You personify chaos in the existence of Superman. Events pertaining to the Man of Steel are transpiring on a course I alone have set. There is no room for deviation. No random element must be allowed to derail what has been put into play."
The imp's time in the prison exposed that Oz exists in "nothing but nothingness" (to use Mxyzptlk's words). Readers were shown that the prison is "negative space" that "nullified" the imp's powers. And when Mxyzptlk escaped, he was able to outsmart Oz by hiding in plain sight, making himself fully human and apparently undetectable to Oz.
In Action Comics #962, Mr. Oz managed to intercept the signal from Superman's Phantom Zone projector so he could grab Doomsday before the creature was thrust into the Phantom Zone.
The character appeared to be the post-Crisis version of Doomsday, and Oz enlisted the help of a battalion of minions and fancy technology to help him steal the beast. Oz said in Action Comics that he "thought" he was done with Doomsday, but he ends up going after him anyway.
The name of the upcoming Doomsday Clock might have more than one meaning, but with Oz holding Doomsday himself, the title makes it likely that the creature will be part in the story - possibly even a weapon against Superman.
Soon after Doomsday's capture, Mr. Oz was shown imprisoning Prophecy as well. Readers were told that Prophecy was grabbed simply because he was "in the wrong place at the wrong time."
In Detective Comics #940, Mr. Oz captured former Robin Tim Drake - making all the Bat-characters think the young man was dead - and imprisoned him. "You were reconnecting threads that could not be reconnected," Oz told Tim. "You're so loved, so deeply intertwined, it became crucial that we take you off the field. And that's where you are, Tim. Off the field."
Tim was just about to attend Ivy University, where Ray Palmer is among the faculty. Ray was shown in DC Universe: Rebirth #1 getting into trouble after finding time anomalies, so it's possible Tim was prevented from linking his intelligence with Ray's research.
Tim was shown two more times - once, he cheered because of Mr. Mxyzptlk's escape, but the other time, Tim himself escaped temporarily (although he didn't get far). When he was in the hallway of the prison, just before Oz sent him back into his cell, Tim seemed very surprised by whatever he saw. Was it Oz himself who shocked Tim? Or was he surprised by the identity of one of the other prisoners?
But then, Tim's imprisonment also has to make sense for the future of the DCU. If Oz had not grabbed Tim when he did, the young hero would have died. Why does Oz need him to stay alive?
Who are the mystery prisoners?
Besides the prisoners we know are being held by Mr. Oz, there are a few other theories floating around about who else is in Oz's prison:
Future Tim Drake (from Batman Beyond)
In the same month that Tim Drake was captured, DC showed the future, older version of the character disappearing in Batman Beyond as well. Series writer Dan Jurgens confirmed to Newsarama that Tim's future disappearance is related to the imprisonment of current-day Tim by Mr. Oz.
Although that appears to mean that Oz's removal of Tim from the current-day playing "field" affected his future, it could also be argued that Oz grabbed both versions. After all, the future that Tim influenced (in early issues of "Rebirth"'s Batman Beyond) didn't change back to what it was before he got there. So he seems to have existed in that future. He only disappeared after those events. So…could an older, future Tim be in one of the cells? Is that why younger Tim was so surprised, because he saw his future self?
The last Martian has been missing from "Rebirth" so far and would be a powerful foe for any attack from the world of Watchmen. And we know he existed at some point in Rebirth's newly merged-together version of the DCU, because his costume was shown within the JLA headquarters during "The Button."
Plus, with all the references to Dr. Manhattan being on Mars (insinuated in both DC Universe: Rebirth #1 and "Superman Reborn"), it might behoove the invaders to keep J'onn J'onnz out of the picture.
Yes, we've already shared a theory about Booster Gold in "Rebirth" that imagines the post-Crisis version of the character still being Waverider (from "Convergence") — and thus connected to the timestream.
However, even if that's true, the "New 52" version of Booster Gold hasn't been seen at all in "Rebirth."
But let's be honest here — any version of Booster Gold would be a serious threat to someone trying to mess with the DCU timeline. Booster is a time traveler, and he's all about time anomalies.
Then again, if the DCU's future really is in jeopardy — if the Legion is wiped from existence (as Saturn Girl implied) and all of DC's future is gone along with them — then Booster wouldn't even exist. So maybe he's gone from the DCU because of DC's shaky history, or maybe Oz put him into her prison because he functions outside time and would mess up his plans.
In DC Universe: Rebirth #1, Ray Palmer was shown trapped in the microverse while investigating "a disruption deep within the temporal nanostructure of the time line."
He contacted Ryan Choi and told him, "I found evidence of something much bigger than a few historical robberies within the very essence of time," and he shrunk down so far that he discovered the "microverse." Palmer asks Choi to similarly shrink down to come rescue him, but he says that Choi needs to watch out for someone.
Who does Choi need to watch out for? Could it be Oz? And could Ray Palmer be not only trapped in the microverse, but imprisoned?
In a recent issue of Justice League of America, Ryan Choi heard something while he was shrunken down and wearing his Atom suit - a voice that appeared to be trying to communicate - although it wasn't clear if it was a clue about Ray. However, the solicitations indicate the "Crisis in the Microverse" storyline by Steve Orlando and Ivan Reis - which is reported to include the rescue of Ray Palmer - won't start until August. And the use of the word "Crisis" certainly adds weight to the story's importance.
Geoff Johns has stated that his story is not a sequel to Watchmen, so theoretically, this could take place at any time before, during or after the events of Watchmen. So all characters - even those who died in the pages of Watchmen or even Before Watchmen - are on the table.
If Mr. Oz is Ozymandias, as many readers suspect, an imprisoned Watchmen character would be a good for the character who was behind the large door from Oz's earliest appearances. Oz seemed to want to talk to that prisoner and acted as if he knew what the character's opinion would be. This suggests a familiarity that might point toward a Watchmen character - if Mr. Oz is indeed Ozymandias.
Other missing "Rebirth" characters
Bart Allen, Shazam, the Spectre, and Kon-El - these characters haven't been seen in "Rebirth" and would all be important to the fight against a Watchmen invasion. Bart's upbeat personality might feed into that idea of fighting hope, and Shazam, Spectre, and Superboy would be powerful enemies for any attackers.
Kon-El and Bart are also attached to the future (or, at least, the "New 52" versions are), so that might explain their disappearance (or maybe their imprisonment). Kon's part of the Superman family, which has fascinated Oz since he first came on the scene. And both Bart and Kon-El are favorite characters of "Rebirth" architect Geoff Johns.
There are countless other characters missing from the DCU (both past and present), so the list could go on and on.
Who else might be in the Oz's prison, and why?