Fan CastingDC’s Tales From The Dark Multiverse Episode 1:

The Batman Who Laughs is a version of Batman from Earth-22 of the Dark Multiverse. In that reality, the Earth -22 Joker learns of Batman's identity as Bruce Wayne and kills most of Batman's other rogues, along with Commissioner Gordon. He then subjects thousands of Gotham City’s citizens to the chemicals that transformed him, subsequently killing several parents in front of their children with the goal of turning them into a combination of himself and Batman. When Batman grapples with the Joker, it results in the latter's death as Batman is exposed to a purified form of the chemicals that gradually turn him into a new fusion of Batman and the Joker, one with Bruce Wayne's intelligence and physical strength and the Joker's psychopathy and warped, sadistic sense of humor. The process proves irreversible by the time Batman discovers what is happening to him. The Batman Who Laughs proceeds to take over Earth-22, killing off most of his allies and turning his son Damian Wayne into a mini-Joker and recruiting the children infected by the Joker Toxin as his "Rabid Robins". The Batman Who Laughs seems to be the leader or second-in-command of Barbatos' Dark Knights and recruits the other members.