"The Joker was killing people. He likes this masked vigilante type and that was how he was getting her attention, was terrorizing their city. And there wasn't - I could have laid down all the ground rules of Mars on that world, and as long as I wasn't sticking around to babysit him and patch holes, he would have found something else to do that would've been distinctly not-benign. I have my own world to babysit, but I found someone from his who let me in to - sequester him. The asylum wasn't going to hold him; he told me as much himself. I did not have another way to keep people around him safe. But I did make sure that he could still visit Milliways in his dreams, from the asteroid, before I left." She shrugs. "You've got a Bell. You don't have to kill anyone to get her attention. She's got enough projects to keep her fascinating for an eternity. And if you go some manner of glitchy and become dangerous anyway, she can take care of it, I don't have to. No one on the Joker's world was going to be able to do anything of the kind. No magic there."