WARNING: This article contains spoilers for Justice League #8 by James Tynion IV, Mikel Janin and Jeremy Cox, on sale now.
When Lex Luthor first brought the Legion of Doom together, he said that he had locked a monster in the basement. In Justice League #8, Luthor and his Legion are reeling from their defeat at the hands of the Justice League. The good guys reached the Totality first, but that doesn't mean the war is over. It is finally revealed that Luthor has been keeping the Batman Who Laughs locked up, and he has been doing so for a very important purpose.
While the Legion of Doom continues its quest to unlock the seven secret forces in the universe, Luthor needs something of a pep talk from the evil Batman. If he has dedicated so much of his time to the universal concept of entropy, how did he still fail in his mission? If he has done something wrong, he's going to need advice from one of the most powerful forces in creation. In the end, the two come together, strike a deal and the Batman Who Laughs reveals a dark secret about the universe.
Lex Luthor Makes a Deal with the Devil
The Batman Who Laughs has proven to be one of the most dangerous creatures across multiverses. He has destabilized and destroyed whole universes in his quest to spread chaos, and has proven to be an incredibly dangerous being to be around. To this end, it makes sense that Lex Luthor would chain him up in an attempt to keep his power in check, even if the two seemingly want the same things.
As it turns out, Luthor was not keeping the evil Batman against his will. He may seem more cosmic Joker at this point, but he's still a Batman. This means he has his own machinations and has only been sticking around because it's where he wants to be. He defiantly spits a lock pick at Luthor to prove this point, but what exactly does this Dark Multiverse Batman want?
He tells Luthor that he has watched his journey with the Legion of Doom to this point. He saw how much he discovered on his own, from the secret plans under the Legionnaire's Club to the secret forces behind creation. However, the Justice League still triumphed because Luthor has yet to truly embrace his new mission, like the Batman Who Laughs has. He also still doesn't have all the answers, so the evil Batman is there to provide them.
The two come to an understanding. If Luthor lets the Batman Who Laughs go, he must understand that the cosmic villain has his own plans. In return, Luthor will receive an important hint about the secret of creation that can help him defeat the Justice League once and for all. The two strike a bargain. The Batman Who Laughs will be released, and Luthor will hear about what is behind the Source Wall.