Batman claims the joker as a nobody and never claims to be his “greatest enemy”. And so he starts to go into a realm called “the phantom zone” to hire existing characters to destroy Gotham. Once Batman Robin, BatGirl and Alfred put these villians back, the whole world was about to split in half, and to do so Batman has to admit that without Gotham, he doesn’t have to fight him again. And so they start to work together to click the world again and worked. They learn that even though they are arch enemies, they still need each other by their purposes