The Grim Knight

The Grim Knight is a gun-obsessed version of Batman from the Dark Multiverse who is assisting The Batman Who Laughs with his criminal activities in Gotham City. He is a major antagonist in The Batman Who Laughs mini-series of comics.

The Batman Who Laughs Mini-Series
The Grim Knight first appeared before two security guards who both mistaken him their world's Batman. One of the guards walked up to greet him but was immediately killed by the imposter before the villain proceeded to gun down waves of reinforcements using his own hefty arsenal. The Grim Knight soon came across Mr. Freeze's cell where Freeze commented on his behavior and tried to provide him with some helpful advice. However, The Grim Knight responded by blasting Freeze with a flamethrower before he made his way over to the Joker's cell and unlocked it. The Joker grinned as he asked The Grim Knight if he was here to kill him too. But the gunman denied this and stepped aside to allow The Batman Who Laughs to do the deed instead.

Later, it is reported that both villains killed almost everyone at the Arkham Asylum, although Mr. Freeze managed to survive The Grim Knight's attack while the person murdered by The Batman Who Laughs in Joker's cell wasn’t the Joker, but an imposter. Batman (of Prime Earth) theorised that Laughs must of snuck The Grim Knight into their world during Barbatos' invasion of the DC multiverse and has been waiting for the right moment to use his talents.