At the conclusion of the original Dark Nights: Metal series by Scott Snyder and Greg Capullo, The Batman Who Laughs lost his fingers. The Joker chopped off the fingers of the interloper, leaving him with a bloody stump.
However, when The Batman Who Laughs returned in the series by Scott Snyder and Jock, his fingers had seemed to have returned as well. Did he regrow them? Are they prosthetics? Could it be a sign that this The Batman Who Laughs was from a different Dark Dimension than the original? Or even from a different point on the timeline?
Certainly, this The Batman Who Laughs was happy to show off his slender digits. Check out this scene from the current Batman/Superman run.
So what happened? Well, during the DC Universe community AMA with Scott Snyder, he was asked about it. "Was this a mistake, did he use dionesium, or is there another solution?" Snyder replied "We thought about that. FULL DISCLOSURE: It was a slip up on my part that I didn't let Jock know in time. So yes, BMWL DID use dionesium."
Dionesisum being the DC Universe metal with healing properties. It is used in the Lazarus Pits, gives the Joker some of his resilience and was used by the Court Of Owls to bring Talons back from the dead. And now with added finger growth abilities.
Scott Snyder also talked about how The Batman Who Laughs would be used in the first issue of the sequel Dark Nights: Death Metal. He told us "the end of issue one had the whole DC office emailing. I'm very aware that he's been in a lot of stories this year for DC and the last thing I'd want to do is use him one more time in a similar way to how he's been used. So expect us to try something very different with him."