[WARNING: This article contains SPOILERS for DC's Legends of Tomorrow]
When you're building an entire ensemble adventure series on traveling through time to prevent disasters caused by traveling through time, ironclad logic or rational physics go out the window. That's a fact that every fan of DC's Legends of Tomorrow has learned already, as the show combated a single enemy throughout past, present, and future in its first season, and now takes on the triple threat of the Arrowverse's own Legion of Doom. And it turns out they're not the only CW cast members searching for the villains, after all.
That's right, the Black Flash has returned after being dishonorably dismissed in The Flash's second season. And in a strange twist of fate, the villain is now determined to hunt down and destroy The Flash's first big bad, Eobard Thawne. Why? How? And in what new form? Those are answers most viewers are bound to be asking themselves, so we're going back in time (not sorry) to follow this new revelation from the very start. And, in keeping with the time travel them, giving our prediction on where the story will ultimately end.
So take notes, and try not to scramble your brains as we do our best to see Black Flash's Return on Legends of Tomorrow Explained.
Zoom's Transformation Into Black Flash
It's hard to forget for fans of The Flash, but the man who joined the cast as the lovable, trustable, totally heroic Jay Garrick turned out to be a monster in disguise. In a clever sequence of baits and switches and combination of multiple Reverse-Flashes over the years, the speedster was revealed to actually be Hunter Zolomon, a villain consumed by his lust for speed, power, and all-around evil. Having injected himself with dangerous drugs to amplify the Speed Force flowing through his cells, Hunter eventually gave himself a new name: Zoom.
As terrifying as he was, his story ended like so many others before him when Barry Allen and his scientifically-minded friends played a bit fast and loose with time itself. Barry knew defeating Zoom in a race was impossible, so he traveled back in time to inform his younger self of the sacrifice he would have to make. Taking on Zoom with two heroes won the day (at the cost of the time remnant version), but it wasn't actually The Flash who took Zoom down for good. No, that fell to the sudden arrival of Time Wraiths - ghostly, ghoulish specters who policed the Speed Force to punish those who would use it to remake the universe, or otherwise 'mess' with it for their own benefits.
Barry's creation of a Time Remnant of himself was effectively bait to attract the Wraiths. Once they set their eyes on Zoom - the real reason for all these Speed Force modifications and abuses - they encircled him, drained him of his energy, and carried him into the Speed Force by... well, force. The result for the heroes was a victory. The result for Hunter was being reduced to a skeletal husk, and sparks of electricity from the Wraiths turning his once-black accents and Flash insignia blood red. Fans of The Flash believed him gone, but fans of the comics knew that his final appearance implied a return could be possible...
Zoom Returns To Legends of Tomorrow
We'll head now to the most recent episode of DC's Legends of Tomorrow, when the long-running question of why a speedster like Eobard Thawne would be in a hurry if he's fast enough to achieve time travel was finally answered. Sure, he may want to avoid the Time Wraiths, but Eobard's fear was far more... present. As Malcolm Merlyn and Damien Darhk finally manage to capture Thawne in one spot to grill him over his hurried demeanor - in an effort to level the playing field of their partnership - Thawne was much less forthcoming with an explanation than the Legends themselves, deducing the cause on their own.
The only answer to why a mystery speedster capable of altering time would instead want to alter reality is that he's running from something, not to something. Something elemental, and terrifying. Something out to erase Thawne from existence, and capable of tracking his use of the Speed Force, no matter where he might run to. As this monster arrived on the scene outside of the Legion of Doom's impromptu meeting, Thawne spilled the beans: the being was a user of the Speed Force just like himself, and had been chasing him ever since he escaped captivity at S.T.A.R. Labs.
To be specific, ever since Eobard Thawne had completed his first trip from the future back to the days of Barry Allen, discovering the famous superhero's true identity, and setting out to return home in an effort to being a supervillain career against the very same man. It's a scary story, and the monster lives up to his reputation... but taking one look at the suit and skeleton beneath it, and it's clear: that's Hunter Zolomon, right down to the mask personally torn by Barry Allen. (Since we're sticklers for detail, the effects team clearly decided the white chest insignia may be too obvious).
Since it's the use of Speed Force Zoom-- or this grotesque, tortured, Black Flash is tracking, Thawne's partners instruct him to stop channeling it entirely. The plan works, with the Black Flash unable to pin down his target, before being ambushed by all three and temporarily trapped inside a vault. The nightmare is briefly contained, but if the Legends' theory behind the Black Flash's motives are true, he's determined to kill Thawne for reasons he can't undo.
Why Eobard Thawne?
As the Legends begin to theorize, Professor Stein shows up with firsthand experience about the speedster who must be aiding Darhk and Merlyn. Having gotten to know the heroes of The Flash during his friendship with Ronnie Raymond, and their combined battles against the Reverse-Flash as Firestorm, he also knows the reason why Thawne's time must be running out. It all goes back to the most convoluted, or simply hard-to-follow bit of time travel fiction introduced in The Flash's first season. And it begins when Detective Eddie Thawne put a bullet in his chest to prevent him from ever starting the family line that led to the supervillain endangering his friends.
The theory was sound, and simple enough for every viewer to grasp: if Eddie dies, Eobard is never born. As clear evidence of his existence being erased, Thawne dissipated into the same vapor-like blue energy seen when Barry tore open time with the Speed Force. The massive wormhole that soon opened up over Central City kept them from dissecting the theoretical physics or philosophy behind Eddie's sacrifice, but fans soon started clarifying the finer points. If Eobard was never born, why wasn't this Earth's timeline re-written entirely? If he wasn't born, he couldn't have killed Barry's mother, meaning everything would have to change...
Yet the universe remained as it was. And more information only arrived once Eobard Thawne came rushing back into their lives. Not the one who they had known before, but his younger self, taking his first trip back in time to the 21st Century. Realizing that Eobard lived, because he had not yet died (from his perspective) defined this villain lost in time as a Remnant himself. Or, as the Legends now call him, an "aberration." Apparently, his connection to the Speed Force granted Eobard a brief loophole through which to remain in existence. But he's had to keep running just to keep existing, since his own non-existence will "catch up to him" if he doesn't.
If it isn't clear just yet, we are squarely in the territory of roughly-sketched science fiction and time travel, in which the specifics are hard to pin down, and the rules governing it only slightly clearer. The bottom line? Thawne has become a dangling thread in the timeline. Since he's a product of the Speed Force, it's the Speed Force trying to correct the mistake. Only this time, they're not sending Time Wraiths, but the speedster they corrupted from Hunter Zolomon into this new, Black Flash.
DC's Black Flash is... The Speedster Reaper
No need to look anywhere other than the comics for clarity, since the Black Flash has long been a terrifying symbol in the world of DC's super speedsters. He isn't actually a person, or even a former speedster reduced to his skeletal form (not that we know, at any rate). The Black Flash is essentially the Grim Reaper for speedsters, appearing shortly before their deaths as a sign that they will soon perish, and return the energy given to them by the Speed Force back to its source. In some stories, the Black Flash has been avoided or outright defeated as the actual cause of a speedster's death, but more often, it's an agent of the Speed Force in the most metaphysical, mystical terms.
That being said, it's not out of the realm of the fiction for a) Hunter Zolomon to be transformed into the Black Flash, or b) be used to track down and kill a speedster whose power should have returned to the source. When Barry Allen return to the DC Universe in The Flash: Rebirth, he was even turned into the Speed Force's new Black Flash before defeating the real villains of the story. If The Flash and Legends of Tomorrow were keeping to the rules of the comics, then the Black Flash (if Hunter has really been given that identity, as it appears) would only be visible to those connected with the Speed Force.
But both Darhk and Merlyn can see and attack him, meaning something else is at play - or an invisible villain is just too unnecessarily complicated for the story. Therefore, the most obvious interpretation or explanation is a happy one, where other speedsters and heroes in the Arrowverse are concerned. The Black Flash has no quarrel with speedsters playing by the rules, and we doubt many will shed a tear when Eobard Thawne finally gets what's coming to him. And for Barry's sake, let's hope no speedster agrees to take his spot beneath the black.