This will be Kevin Conroy's final vocal performance for a movie as Batman that will be released posthumously since his death in 2022.
The last performance of Mark Hamill as Joker, due to his retirement for voicing Joker because of Kevin Conroy's death in 2022.
The final chapter of the Tomorrowverse of DC Comics animated features, which started with Superman: Man of Tomorrow (2020).
This is the second adaptation of "Crisis on Infinite Earths" after the CW's DCTV crossover, which consisted of Crisis on Infinite Earths: Part One (2019), Crisis on Infinite Earths: Part Two (2019), Crisis on Infinite Earths: Part Three (2019), Crisis on Infinite Earths: Part Four (2020) and Crisis on Infinite Earths: Part Five (2020) on Arrow (2012-2020), The Flash (2014-2023), Supergirl (2015-2021), DC's Legends of Tomorrow (2016-2022) and Batwoman (2019-2022).
Having all the different Worlds inside the Bleed dimension is causing them to literally bleed into each other; similar to Incursions from Marvel Comics. This lets dinosaurs and Nazis (no surprise) to complicate things.