WARNING: The following article contains spoilers for Justice League #57, by Joshua Williamson, Xermanico, Romulo Fajardo Jr. and Tom Napolitano, on sale now.
After being betrayed by Perpetua in the lead-up to the crossover event Dark Nights: Death Metal, the Legion of Doom are officially unleashed and hungry for revenge against their omnipotent benefactor. Trapped inside Perpetua's throne and destined to be converted into raw fuel as the villain launched her rampage across the DC Multiverse, the Death Metal iteration of the Justice League has freed their imprisoned foes as the last war for the fate of the multiverse rages on. As the forces of good and evil draw the lines for their final battle, the Legion dusts off one of their biggest weapons ahead of the fight: The Hall of Doom.
Just like their animated counterparts on the Super Friends, the Legion of Doom were headquartered out of a secret lair. Under Perpetua and Luthor's guidance, the various villains were upgraded and united against the Justice League and heroes from across the multiverse. As the Legion of Doom marched against the heroes, the villains revealed that the Hall of Doom was actually a mobile battle station, heavily armed and able to take flight. The vessel engaged the similarly equipped Hall of Justice in the skies above the battle between Perpetua's forces, with both mobile headquarters crashing back down to Earth by the battle's end.
While the Hall of Justice was eventually discovered in Slaughter Swamp outside of Gotham City, the whereabouts of the Hall of Doom had been unknown at the start of Death Metal. Now reunited with his most trusted associates on the Legion of Doom, Luthor summons the Hall of Doom to pick up the villains just as Castle Bat arrives on the battlefield following the Omega Knight's defeat at the hands of Sinestro. This Dark Knight was a version of Batman from the Dark Multiverse that performed an unholy ceremony, sacrificing his own son to merge his consciousness with Gotham as a murderously sentient city recruited by the Batman Who Laughs to help him conquer and oversee the main DC Universe while similarly serving as a mobile headquarters.
Facing assembled heroes and villains working together to topple Perpetua and the Darkest Knight, Castle Bat rearranges itself to become a towering, kaiju-sized incarnation of Batman comprised of the various bits of the city. More than just mobile, the Legion of Doom reveals its weapons systems are also back online, armed and operational. As the Dark Knights' mobile headquarters menaces the heroes, the Legion of Doom's mobile hideout blasts Castle Bat to smithereens, felling the largest of the Darkest Knight's allies in a cascade of rubble as the Hall of Doom takes victorious flight.
The Legion of Doom is working together once again after a lengthy imprisonment inside Perpetua's throne as an unwilling power source. The assembled supervillains have wasted no time in defeating not one but two of the Darkest Knight's most powerful associates. And with the Hall of Doom restored to its destructive potential and the Legion back at the helm, Luthor is well on his way to reclaiming his place as one of the deadliest figures in the DCU after his epic fall from grace -- being isolated and betrayed by Perpetua. With the Hall of Doom rearmed, he's got one hell of a weapon to finally achieve his revenge.