MR. OZ's PRISON: Why Is TIM DRAKE So Important? And Who Are His Fellow Prisoners?
Tim tried to escape:

Poor Tim Drake. Stuck in a prison cell while the rest of the DCU thinks he's dead, Tim is one of the main clues that readers have been given about the nature of the mysterious Mr. Oz and his possible link to the Watchmen invasion revealed at the beginning of "Rebirth" in DC Universe: Rebirth #1.
In September's Detective Comics #940, Tim Drake sacrificed himself to save hundreds of people in Gotham City, reprogramming a slew of missiles to aim directly at him (instead of the potentially innocent people they'd originally been designed to kill).
But - as the missiles impacted the teen hero - Tim was seemingly whisked away by Mr. Oz, the recurring character who's been shown in the latter days of the "New 52" and into "Rebirth" to have been "watching" DC characters.
Tim is now trapped in a cell that has a semi-transparent door, in a prison that's being controlled by Mr. Oz. And readers were shown that Tim is not the only person being imprisoned in this way in fact, there are specifically two other doors (with two other nondescript shapes) in the same hallway of the prison.
Oz is almost certainly connected to the time discrepancies first discovered by the return of Wally West. According to Wally, someone stole 10 years out of the DC Universe and messed with it in other ways, including the creation of the "New 52." The pages of DC Universe: Rebirth #1 made it pretty clear that the "someone" who messed with time is Dr. Manhattan - and possibly other characters from Alan Moore and Dave Gibbons' Watchmen.
Although DC stories so far have not spelled out a relationship between Mr. Oz and the Watchmen characters, Newsarama (and many fans) has speculated that Mr. Oz is actually Ozymandias from the Watchmen universe.
Whoever Oz is, he explained that he grabbed Tim Drank out of the the DCU because he was "reconnecting threads that could not be reconnected. 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."
]So what threads were being reconnected by Tim Drake?
Brilliant Detective
Although it's true that Tim is "loved," as Oz mentioned, the character has also always been portrayed as a particularly accomplished detective. And recently, he's been shown to be a technical genius. But his greatest threat to Mr. Oz might be his insistence on finding the truth, even if the truth seems impossible.
In particular, when Bruce Wayne died, Tim Drake was the only character who didn't believe he was really gone. And he investigated that idea obsessively, eventually find out that it was true.
If Tim Drake was about to discover something, or had maybe even found something that piqued his interest, Mr. Oz could rightly-assume that he would investigate it until the bitter end.
And that's could be the reason for Tim's kidnapping by Mr. Oz. But what did he find that set Mr. Oz off?
Future Tim
Readers will also remember that, when "Rebirth" began, there was a second version of Tim Drake in DC books – one who was trapped in the future, and who had donned the futuristic costume of Batman in DC's Batman Beyond title.
However, at the end of September's Batman Beyond #16, Tim Drake disappeared after he turned over the mantle.
When asked if this "future" Tim's mysterious disappearance would be explained at some point, Batman Beyond writer Dan Jurgens said it would.
"Of course," he said, "though, as with many fun story elements, it might take a while."
And is the older version of Tim's disappearance from September's Batman Beyond related to the younger Tim's disappearance from Detective Comics the same month?
"Yes," Jurgens confirmed.
So Mr. Oz probably didn't just grab Tim out of the present day DCU, but his action somehow nabbed Tim out of the future as well.
Perhaps the "connections" he was figuring out were related to his future self?
Ivy University
Just before he was taken by Mr. Oz, Tim was preparing to go to Ivy University, which also just happens to be the place where Ray Palmer (The Atom) teaches, and where Ryan Choi is his trusty sidekick student.
Since the beginning of "Rebirth," Ray has been trapped somewhere in what he calls the "Microverse." In DC Universe: Rebirth #1, Ray sent a message to his assistant Ryan Choi stating that he was in "big trouble" and needs rescued. And the reason that he became trapped? He was investigating "a disruption deep within the temporal nanostructure of the time line."
"I found evidence of something much bigger than a few historical robberies within the very essence of time," Palmer said in the message.

Palmer told Choi that he shrunk down so far that he discovered the "Microverse." He asked Choi to similarly shrink down to come rescue him - and DC has revealed that Choi's search for Ray is going to take place within the new Justice League of America title launching in February.
Newsarama has speculated in the past that Ray Palmer is actually imprisoned in Mr. Oz's prison. After all, Palmer was investigating time anomalies, which seem to be associated with Mr. Oz. Palmer also told Choi that the student needs to watch out for someone during his shrunken journey (although his transmission was cut off before he could describe who should be avoided). Lastly, the wall behind Ray Palmer during his transmission looks a lot like a prison - even a little like the place where Tim's imprisoned.
Two Prisoners
There have been a lot of speculation about who the other two prisoners are, shown at the end of Detective Comics #940 and #947. As stated earlier, it's possible that Ray Palmer is in the same prison, and other guesses have ranged from "New 52" Superman and Superwoman to the Doomsday character that Mr. Oz during the first few months of "Rebirth."
But James Tynion IV, the writer of Detective Comics #947, made it clear that Tim was absolutely dumbfounded by what he saw when he briefly escaped into the hallway of his prison.
"What...that's not possible," the shocked character said. "That's...I don't...I don't understand."
As we've already mentioned, Tim Drake's a pretty brilliant young man. He wouldn't be shocked and confused by just any sight. So what did he see?
Was it something in the hallway? Or was it the two other prisoners?
And if the two other prisoners were the ones who shocked and confused him, what two characters would do that to young Tim Drake?
Probably not Doomsday. Maybe not even Superman (even though he was aware of his death), and certainly not Superwoman. Mr. Oz is definitely interested in things involving Superman - it's his titles where he's been seen for the most part, until Tim's kidnapping. But the reaction by Tim in Detective Comics #947 indicates that whatever he was much closer (or more meaningful) to the character.
Perhaps one of the other cells holds his older self from Batman Beyond? But would Tim recognize himself that suddenly and be that confused?
Tim tried to escape: