Dark Nights: Death Metal Legends of the Dark Knights #1

Synopsis

The Batman Who Laughs recounts his life from seeing his parents murdered to becoming the Batman to avenge their deaths, then to killing the Joker on his world, only to have the Joker's body release a toxin upon his death transforming Batman into The Batman Who Laughs, who then killed all the heroes on his world before turning his attention to Earth 0. When he is killed by Wonder Woman, he had arranged to have his brain transplanted into the body of Batmanhattan by the 3 Alfreds from the Dark Multiverse, and now he as he fully explores his cosmic powers, he evolves into the Darkest Knight.