WARNING: The following contains spoilers for Detective Comics #1051 by Mariko Tamaki, Max Raynor, Luis Guerrero, and Ariana Maher, on sale now from DC Comics.
Arkham Asylum has had its fair share of wildly powerful inmates. The likes of Poison Ivy and Clayface are a given but it's also seen powerful people like the Legion of Superheroes' Saturn Girl enjoy a brief stay. Now it looks like the new Arkham will have the most powerful inmate of all - Darkseid. And it's all thanks to one other powerful patient.
The mystery behind Arkham Tower's miraculous mental health treatment was revealed in Detective Comics #1051. It was Psycho-Pirate making everyone in the facility calm this entire time. He was recruited by the head of the facility, Dr. Wear, who turned out to be a conman named Tobias. Tobias was looking to con the city out of its money by creating Arkham Tower and faking a perfect cure for Gotham's mental health crisis. He saw Roger Hayden and the Medusa Mask as the perfect way to do it, but Psycho-Pirate was much more concerned about something else.
Psycho-Pirate was last seen in the final issue of the Infinite Frontier limited series by Joshua Williamson, Xermanico, and various other artists. There he was recruited by Darkseid to force the Flash to run in the New God's mysterious multiverse machine. When that failed and Barry Allen ran off, creating a crack in the multiverse, Darkseid blamed Hayden. Rather than wait to be blasted into oblivion by the Omega Beams, the Crisis villain disappeared, with the ominous and slightly-comical words "I'm needed in another event."
Psycho-Pirate has featured in every DC Crisis in some form, so it was expected that he really would next appear in whatever cosmic calamity is coming next. As it turned out, he simply fled to Earth and hid. He clearly didn't take Darkseid's anger lightly and genuinely feared whatever punishment will come from his failure.
When he isn't participating in massive reality-altering cosmic events, Roger Hayden is just a simple criminal. He may know the secrets of the universe and have an ultra-powerful mask that can make anyone feel any emotion he chooses but that doesn't change his roots. Therefore, he agreed to help Tobias with his con and is in Arkham once more, just not as a patient this time. That's exactly why Darkseid might become its next inmate. He may be all-powerful but he's also clever. His fate has also been left uncertain by the latest issue of Justice League Incarnate so who knows where he could next appear.
It's likely that Darkseid will want to raise an army for whatever cosmic calamity is coming up next. With a score still to settle with Hayden, why not kill two birds with one stone and settle both at Arkham. Darkseid has favored both the conspicuous and the inconspicuous in the past. It's possible that he or one of his followers could disguise themselves as an inmate and only reveal their plans when the time is right. It's also possible that he and his Parademons could just full-on assault Arkham Tower, eliminate Psycho-Pirate and recruit any Gotham rogues to that take his fancy.
Regardless of the what-ifs, Psycho-Pirate seems to believe the hordes of Apokolips are coming for him. If they do, it's likely that Gotham will become a war zone and Arkham could be the perfect battleground. Many of Gotham's worst villains would fit right in with Darkseid's troops and seeing them get a cosmic upgrade could make the next big Crisis all the more interesting.