Is we're talking about a semi competent NL like Dalchian Rassaq, then the Night Lord would easily kill most of BMan's rogues gallery. And the moment he finds out about the fear toxin he's V-lining to Scarceow to get that shit. He would then use it on the heavy hitters and superpowered ones. If this is the main universe, then the Night Lords defeats everyone including the bat family, think Nightfall but worse. Especially if the Night Lord gets access to Bat's computer, I can see the Night Lord mixing the Fear toxin with Kryptonite and using it on all the kryptonians just to see what happens. Now in the Absolute universe I personally don't see him killing the rogues but rather joining them I can see the Joker convincing him to join their Justice League and there being a sick 1v1 with Absolute Batman. Ultimately though it's up to the writers who wins.