The Flash is known to drop multiple plot threads due to editorial shifts and edicts.
Comic Books
- Back in Messner-Loebs' run, Wally's surrogate father figure Mason Tollbridge had Ship Tease with Joan Garrick when Jay was believed dead, and the two received significant panel time together. This went out the window when Mason married a New Old Flame and was subsequently Put on a Bus, with his entire role as Wally's mentor/surrogate father being replaced by the recently-revived Jay Garrick when Mark Waid took over.
- Early during Geoff Johns' run, Detective Jared Morillo was stabbed by Cicada's blade, granting him a speed-derived Healing Factor. This continues to be a major that he only shares with Fred Chyre, and they indicate that he's now connected to Cicada mentally. This plot never goes anywhere, however, as Chyre and Morillo are Demoted to Extra when Wally's identity becomes a secret again.
- Iris West and Fred Chyre were shown to have a budding Ship Tease, after Iris adopts Fred's godson before he could and the two bond while taking care of the boy. Besides Wally's confused response, this also goes out the window when Wally's public identity is erased.
- After the identity erasure, Wally becomes a suspect in a criminal investigation when he forgets to finish repairing Ashley Zolomon's brakes, nearly killing her in a car crash (at the same time, Linda had walked out on Wally over the identity erasing, and with no one to vouch for her whereabouts, the police suspect Wally snapped and killed her). This plot got significant build-up, but after Wally and Ashley have a heart-to-heart and Linda returns, it never comes up and Morillo and Chyre all but completely disappear.
- Meloni Thawne had left a message for Bart Allen (the fourth Flash) to stay away from his brother. While Bart didn't know it at the time, Meloni was referring to Owen Mercer, the second Captain Boomerang. Owen even inherited super speed and was learning to use it more efficiently (he could only do small bursts initially). It's implied that this may have had something to do with the Rogues killing Bart...except Owen wasn't even a part of that group at the time. Bart would later return to life and Owen would die, and this warning about their meeting could never occur. In fact, they never even met.
- In Impulse #88, Max Mercury is possessed by the spirit of Edward Clariss aka the Rival, and dragged off to an unknown destination in time. This was never followed up on thanks to the book being cancelled. Max would turn up in the Speed Force during Infinite Crisis before being brought back in The Flash: Rebirth but Clariss’ fate was never revealed and he never appeared again before Flashpoint
- The Flash: Rebirth left multiple sequel hooks that weren't followed up on:
- The ending implied that the Reverse-Flashes of the Silver and Modern Age would be teaming up again (they had briefly worked together once previously in Rogue War). Hunter Zolomon, the second Reverse-Flash, had lost his powers but approached Eobard Thawne, the first Reverse-Flash, and told him that they could make each other "better". Within the story itself, Eobard had used one of Hunter's signature moves and even explicitly said he learned the trick from Hunter. Then Flashpoint, a Flash story by the same writer rebooted the DC Universe, and Zolomon and Thawne didn't exist in this universe for years, as a new Reverse-Flash was introduced and seemingly was the first. Later, Eobard would be reintroduced (and even later, he'd regain his pre-Flashpoint history and memories) and use some more of Hunter's signature moves. About a year later, Hunter would return, but by the time Hunter returned, Thawne was dead! However, the prison scene was eventually followed up on, close to a decade after it happened — Eobard broke Hunter out a while later and explicitly brings up Hunter's offer, and we learn that Eobard and Hunter travelled into the future and worked together before a disagreement divided the two, and Eobard ended up dead, leading to Hunter's Roaring Rampage of Revenge on the Flashes in "Flash War".
- Thawne told Wally West that one of his kids would grow up to ruin his life. Wally's son Jai had lost his powers to his sister Irey (and also Took a Level in Jerkass compared to what he had been like before the miniseries), and the ending implied that he was now The Resenter because of his sister now having full access to superspeed and being allowed to be part of the Flash Family. There were plans for a Green Lantern Corps-esque series called All-Flash, with Wally West serving as protagonist with numerous Flash characters in supporting roles while Barry Allen kept the main Flash ongoing, and Wally's son Jai was meant to become the new Turtle after his disconnection from the Speed Force altered him and gifted him with the ability to steal speed, similar to his father. The series never happened because DC were worried that the name "All-Flash" would be too easy a target for critics (i.e. "All Flash, no substance"), and the plot point of Jai's depowering was never brought up again. Then Flashpoint rebooted Wally and his family out of existence. When the twins eventually did return, Jai not only had a Speed Force connection, but now had superspeed. Interestingly, the final issue of Doomsday Clock featured an image of what appeared to be Jai in a Turtle costume as part of a vision of the DCU’s near future. However, since this whole spread was meant to foreshadow the now-cancelled "Generation Five" initiative, it seems Jai/Turtle subplot has once again been abandoned. A story in The Flash (Infinite Frontier) depicts the adult versions of Irey and Jai, and Jai is said to be a superhero there with superspeed, and later on would regain his super strength abilities.
- It was said that Thawne had done something to Gorilla City's jungles...again, not followed up on.
- Abra Kadabra returns at the end of the series, saying that he'd been put out of commission by Thawne himself. He is seen preparing a plan that will involve all three Flashes, as well as both Reverse-Flashes. Nothing ever comes of it.
- The Flash (2016) had an annual that set up a new life for Wally after he was confined to the Titans ongoing. It saw him reconnect with Magenta and restore her memories and powers of her old life and setup an apartment for himself in Keystone City. He would return to the book proper in the "Perfect Storm" arc, which saw him helping Barry and even being passed the mantle of the Flash again for a while. However, the arc right after that, "Flash War", ended with Wally in the superhero therapy centre, Sanctuary, which led into Heroes in Crisis. There, Wally suffered a mental breakdown and was imprisoned in its conclusion for manslaughter, which seemingly completely derailed whatever Joshua Williamson had planned for Wally.
- In the Flash Forward miniseries, Wally ends up confined to the Mobius Chair which has been imbued with the leftover powers of Doctor Manhattan. The epilogue to the miniseries showed Wally gaining access to knowledge of the various reboots of the DCU and its complete history, with him and Tempus Fuginaut intent on fixing the fractured history of the DCU to create a solidified timeline — which was what the "Generation Five" initiative was meant to do. However, huge shifts in DC's structure led to those plans being scrapped in favour of a Soft Reboot with DC Infinite Frontier, so Wally instead is interrupted before his attempt by the Batman Who Laughs. In the end, Wally's time as "Wally Manhattan" didn't amount to much and his god-like powers were removed, with Wonder Woman instead defeating the Batman Who Laughs, leading into a soft reboot.
Live-Action TV
- The Flash (2014)
- In The Stinger of "Power Outage", Thawne takes a blood sample from the dead body of Blackout, musing that his ability to drain The Flash's powers will come in handy. However, this is never brought up again for the rest of the season.
- Captain Cold slowly forming the Rogues has met an abrupt end since he's been transplanted to Legends of Tomorrow. And now, with his death, it seems this arc will never be completed.
- After the end of the Gorilla Grodd storyline near the end of season 1 General Eiling tells Barry that he is aware of his Secret Identity and that this isn't the last time he sees him. Despite that Eiling has yet to appear in the Arrowverse since said episode.
- In Season 3, Mirror Master and the Top were meant to be replacements for Cold's gang but given the lukewarm reception of their debut they haven't been seen since.
- In Season 3, Savitar says to Jesse Quick that he has plans for her when they meet. This is never addressed or brought up ever again. And with Savitar's death/erasure from existence at the end of the season, it's likely that it will never be addressed again.
- In Season 8 episode 8, Taylor vows to destroy Allegra for undermining her at the Central City Citizen. This B-arc isn't significantly developed, nor is Allegra and Taylor's rivalry explored in detail until episode 17, the same episode in which they bury the hatchet. Taylor only appears four more times in the remainder of the series, including a dream sequence and a scene in which she has no dialogue.
