WARNING: The following contains spoilers for Justice League #54, by Joshua Williamson, Xermanico, Romulo Fajardo Jr, and Tom Napolitano, on sale now.
As a new Justice League is forged in the fires of Dark Nights: Death Metal, the villainous Batman Who Laughs has assembled a new team of Dark Knights to help him reshape and rule over the conquered DC Universe. Among the most devious of the new invaders from the Dark Multiverse is the Dark Mindhunter, one of the Darkest Knight's most trusted lieutenants and a twisted combination of Batman and the Martian Manhunter. And as the evil Dark Knight holds the main DCU's J'onn J'onzz captive, the twisted villain reveals his horrifying origins in Justice League #54.
After being freed from imprisonment on Apokolips, Nightwing leads a ragtag group of heroes to form a Justice League back to Earth. The ensemble is tasked with freeing the Legion of Doom members powering Perpetua's throne, helping fuel her rampage across the DC Multiverse. This mission proves to be far more daunting than they initially anticipated, with the throne protected by the fearsome Omega Knight. To make matters worse, the Martian Manhunter was already overpowered and captured by the Dark Mindhunter as J'onn made his own desperate attack on Perpetua's power source. As the new Justice League rallies together to rescue their friend and complete their vital mission, J'onn faces his Dark Multiverse counterpart head-on.
The Dark Mindhunter reveals he was a version of Bruce Wayne from a world within the Dark Multiverse that coveted the Martian Manhunter's vast powers. Desperate and increasingly unhinged, this iteration of Bruce injected himself with raw Martian DNA to trigger his fiendish transformation into an amalgamation of Batman and the Martian Manhunter, now possessing powerful telepathic abilities, superhuman strength, speed, endurance, heat vision and the abilities to go intangible and change his physical shape as needed. It's the telepathy, in particular, that the Dark Mindhunter was after and continues to employ it against his captive, probing the Martian Manhunter's mind to locate what Wonder Woman and the other heroes are up to as they lead their own coordinated missions against the Darkest Knight.
The process this incarnation of Bruce Wayne undertook to become the Dark Mindhunter echoes how Lex Luthor transformed into Apex Lex at the start of last year's "DC's Year of the Villain." After being freed from the Source Wall, Perpetua tempted Lex with a promise of a cosmic upgrade, leading the megalomaniac to inject himself with Martian DNA. Lex would be reborn as a significantly more powerful figure that upgraded the supervillain community and helped them triumph over the combined might of the DC Multiverse's superheroes before being betrayed by Perpetua and replaced by the Batman Who Laughs as her new vassal. Broken and scarred by the betrayal, Lex formed a tenuous alliance with the Death Metal Justice League as he seeks revenge.
Possessing Batman's keen, tactical intellect and the vast array of powers available to the Martian Manhunter, the Dark Mindhunter is easily one of the most powerful Dark Knights yet, and he will be one of the biggest obstacles for the Death Metal Justice League to overcome in completing their mission. J'onn J'onnz has prepared himself for the possibility of a psychic attack on his mind but the Martian can only hold out for so long before his mental defenses break and the heroes' entire plan to save the DC Multiverse will be exposed to their greatest enemies.