Warning: The following contains SPOILERS for The Flash season 8.
It appears The Flash season 8 has set up a major Green Lantern event from the comics, known as the Blackest Night. Originally published in 2009-2010, Blackest Night was the culmination of several storylines in the Green Lantern comics of the time, but it grew to engulf the whole DC Comics universe. While being a well-regarded event, Blackest Night remained a rather left-field choice to be adapted for the Arrowverse until the introduction of the undead villain Deathstorm.
The second major story arc of The Flash season 8 centered around a mysterious metahuman murderer, whom Dr. Caitlin Snow (Danielle Panabaker) came to believe was her dead husband, Ronnie Raymond (Robbie Amell), confused and transmuted into a new form. The rest of Team Flash was skeptical, despite Caitlin determining that the only common link between the victims, apart from how they died, was that they were all people she knew. Unfortunately, Caitlin's faith proved to be ill-justified, and her efforts to bring her husband back to life only served to give the Black Fire Killer a more tangible form. Referring to himself as Deathstorm, the Black Fire Killer revealed his true nature to Caitlin at the end of The Flash season 8 episode "Resurrection" and that Ronnie Raymond's return as Firestorm was a ruse.
A villainous being with Ronnie Raymond's memories was one of the many monsters created as part of the Blackest Night event in the comics, in which the death god Nekkron sought to take over the universe by raising an army of undead superheroes and supervillains. Later, during the Brightest Day story, which followed Blackest Night, this dark being came to infect the Firestorm matrix and took on the name Deathstorm. While the name of Nekkron has yet to be mentioned in The Flash, the dark powers manifested by the Arrowverse Deathstorm are consistent with his comic book counterpart.
The Flash season 8, episode 11, "Resurrection," also introduced a means through which the dead might be resurrected, as STAR Labs engineer and new Team Flash member Chester P. Runk (Brandon McKnight) reconfigured the quantum splicer which Ronnie Raymond used to stabilize himself and fashion a new body. In this same episode, Chester almost revealed the secret of how to build the device as part of his streaming series offering advanced DIY science lessons to his social media followers. He decided against it, however, after Allegra Garcia pointed out the harm other people without Chester's ethics could do with that kind of technology, stating that death is a part of life and that everyone must eventually face "noche mas negra... the blackest night."
While this would not be the first time The Flash has dealt with an army of superpowered zombies, it seems strange that the show should adapt Blackest Night without a Green Lantern on hand. Then again, the Black Fire story arc may be merely a means toward finally introducing John Diggle as the first Green Lantern of Earth-Prime. If that's the case, it may well justify the convoluted and twisted story the CW's The Flash is currently unfurling.
The Flash releases new episodes Wednesdays on the CW.