Warning! Spoilers for Hell Arisen #4 below! Now in stores.
The Batman Who Laughs' grand plan has come to fruition. The dark multiverse hybrid of Batman and the Joker just executed his most sinister plan yet and is teaming up with Perpetua in order to destroy Earth, it's heroes, and cause irreversible damage to the entire multiverse.
Perpetua created the first DC Universe, however, her thirst for evil and destruction resulted in the multiverse being reformed as the God was imprisoned. She's the mother of the monitors Mar Novu, Alpheus, Mobius, and Overvoid - who observe different parts of the multiverse to prevent their demise. Perpetua was brought back to being by Lex Luthor with the help of other DC villains. In return, Perpetua made him "Apex Lex" a martian/human hybrid with incredible powers and promised him a future he couldn't resist.
In Hell Arisen #4 by James Tynion, Steve Epting, Nick Filardi, and Travis Lanham, Luthor comes face-to-face with the Batman Who Laughs. Lex manages to take him down and cure the dark multiverse Justice League of their infections. He teleports the Batman Who Laughs directly to Perpetua. Lex says with the death of the Batman Who Laughs, the spreading of darkness will allow them to continue their work in reshaping reality. However, the Batman Who Laughs has other ideas. He tells her he's the "child of unreality," and that he can help her see what she can't. As Lex pleads that the evil Batman is lying, the Batman Who Laughs reveals he's captured the Phantom Stranger and the reality Luthor envisioned with Perpetua was a work of fiction.
The Batman Who Laughs bows before Perpetua and tells her she needs a right-hand man, not a "pet" like Luthor. This infuriates Lex, who turns his arm into a sword and lunges at his enemy. However, Perpetua stops him and Luthor's arrogance shines through, calling her "a spark of a power trapped inside a doorknob until I freed you." Perpetua doesn't take kindly to the remarks and turns Lex from Apex Lex back to his human form. As Lex threatens to kill Perpetua, she sends him through a portal. The Batman Who Laughs tells Perpetua she can stop the facade she intends on keeping Earth safe. Perpetua tells him she doesn't trust him, but after reading his mind, she sees those dark things from the dark multiverse that she couldn't see before and starts laughing like the Joker.
It's safe to say the Batman Who Laughs' long-game to getting to Perpetua worked perfectly. He gave her a reason - his knowledge of what she can't see - to team-up with him and ditch Lex. What comes next is going to be huge. Not only is the Batman Who Laughs working with a God, but he's likely going to get an even bigger power upgrade thanks to Perpetua. As Lex tells Mercy Graves after being found on Earth, "we're all dead now." This Batman Who Laughs/Perpetua team-up is going to be cataclysmic for Earth and the entire multiverse.