Warning: The following contains spoilers for Death Metal: Trinity Crisis #1 by Scott Snyder, Francis Manapul, Ian Herring, and Tom Napolitano, on sale now.
After The Batman Who Laughs is killed by Wonder Woman back in Death Metal #1, the Dark Knights set in motion a plan to put The Batman Who Laughs' brain into the body of a new creature. With Wonder Woman putting together her plan to stop Perpetua, one of the heroes senses that something isn't right and there's now a threat that is bigger than just The Batman Who Laughs.
In Death Metal: Trinity Crisis #1, Wonder Woman sets out her plan to the others to stop Perpetua and defeat the Dark Knights. Part of the plan involves storming Castle Bat and finding the nexus point of energy that is supplying Perpetua with all her power. As they set off on their mission and approach the fortress, one of the characters senses an immense presence of evil that they hadn't sensed before.
Jarro's role in the mission is to block the minds of the heroes so they can't be detected. But being the most powerful psychic in the DCU, Jarro senses that "The Batman Who Laughs ... [has] become something much worse." Jarro senses that The Batman Who Laughs has evolved into something even more powerful and diabolical. As noted above, The Batman Who Laughs now has the powers of Doctor Manhattan after his brain was put into what fans call "Bathattan," which is a Bruce Wayne/Doc Manhattan hybrid. In Death Metal: Legends of the Dark Knights #1, it is revealed that on the world where Bruce Wayne found the button of the Watchmen's Comedian, Bruce reverse-engineered the traces of power found on the button and created his own intrinsic field generator. After the experiment goes horribly wrong, Bruce is disintegrated and slowly puts himself back together just like Doc Manhattan did. Now having all the powers of Doctor Manhattan, this is the version of Bruce Wayne that now houses the brain of The Batman Who Laughs.
Because the heroes don't know his new name is "the Darkest Knight," Wonder Woman is the first to refer to him as "The One Who Laughs." She uses this monicker in recognition that they don't know what the Batman Who Laughs has become and what he is capable of. But what exactly has he transformed himself into and what is his plan?
The Darkest Knight is a body of pure energy that is essentially all-powerful and can travel the Multiverse and Dark Multiverse at will. The Darkest Knight plans on stealing Wally West's powers, who was also recently imbued with Doctor Manhattan's powers, to become more powerful than Perpetua herself. He then plans on creating his own multiverse that will destroy all other multiverses, making him not just the most powerful being in the omniverse but the only being with power.
The heroes may not have met the Darkest Knight yet, but thanks to Jarro they are now aware of the powerhouse The One Who Laughs has become. As the heroes' missions start to go south, they all begin to realize the need to alter their plan to account for this powerful new player that is dominating the chessboard.