Every time he runs, Barry Allen runs the risk of completely derailing the time stream. The Flash is the last person who should be entrusted with the powers of the Speed Force. Many times the Flash ended up creating alternate timelines either out of his own foolishness or his blatant incompetency. Here are the ones that majorly affected the Arrowverse.
The Vandal Savage Timeline
In the 8th Episode of Season 4 of Arrow titled “Legends of Yesterday”, the Green Arrow, the Flash, Hawkman, and Hawkgirl come together to stop Vandal Savage, an immortal warlord who is forever cursed to hunt down Hawkman and Hawkgirl. Savage uses the Staff of Horus, an ancient artifact, to destroy Central City in a massive explosion. Barry is only able to escape the explosion because he manages to outrun it. He gains enough speed to travel back in time. This time, with Barry’s expertise, the heroes manage to stop Vandal Savage in his tracks. The alternate timeline where Central City is destroyed and the heroes of the Arrowverse die is never mentioned again.
The Weather Wizard Timeline
This was the first time ever that Barry Allen realized he can tap into the Speed Force to jump back and forth in time. In the 15th Episode of Season 1, Barry Allen fights Mark Mardon aka the Weather Wizard. The Episode titled “Out of Time”, features Barry fighting the second person to hold the mantle of the Weather Wizard. Mardon intends to launch an enormous tidal wave that can destroy the entire Central City. Barry accidentally runs so fat he defies the laws of physics and succeeds in travelling back in time. By doing so, Barry undoes several important events that happened during the episode. Barry kissed Iris for the first time. Cisco figured out Wells’ identity as the Reverse Flash aka Eobard Thawne. Thawne would later kill Cisco. In the next episode “Rogue Time”, none of the events happened. The new reality then became the official timeline for CW’s The Flash.
The Pied Piper Timeline
This is a blink and you miss it event. Zoom’s terror is taking over Central City and the Flash is unable to outrun the new threat. So he decides to travel back in time to find out the secret to unlocking a greater level of speed. To do so, he has to take the help of Eobard Thawne of the past. Tricking the Reverse Flash into helping him is the only way Barry knows of finding a way to eventually defat Zoom. The flash arrives at the same time Hartley Rathaway is fighting the Flash. The Time Wraiths, creatures that protect the time stream and apprehend any speedster that travels through time too much, catch a hold of the Flash’s scent. When Barry travels back to the present, a Time Wraith follows him. But due to Barry’s meddling in Rathaway’s past, the Pied Piper is now one of the good guys. That does not stick for long since Rathaway is back to being a villain Post-Crisis.
The Post-Flashpoint Timeline
The Flash did everything in his power to undo his mistakes when he created the convoluted Flashpoint timeline. But things did not become normal when Barry tried to fix time. Instead in some aspects it was worse than the Flashpoint timeline. The many changes that remained the primary elements of this timeline were the creation of the Cult of Savitar, Caitlin Snow’s Killer Frost personality, and Julian’s entry into the Central City Police Department. The Post-Flashpoint timeline changed Sara Diggle to John Diggle Junior. The complications created by the Post-Flashpoint timeline were then erased after the Crisis Event shook the very core of the Arrowverse. The only element from the Post-Flashpoint that struck around was the Killer Frost persona of Caitlin Snow.
The Savitar Timeline
The timeline is mentioned in only but name. We have a brief glimpse of this future only when Savitar mentions it when he speaks. In this timeline, Savitar is able to kill Iris West. Team Flash continue fighting Savitar. The super villain eventually defeats Team Flash in this reality. The Flash uses a last ditch effort by creating multiple time remnants of him-self to overwhelm Savitar. The plan works but most of the time remnants die. All but one Time Remnant Barry survives the event. This version of Barry would eventually let darkness into his heart and become the villain Savitar. In the Post Flashpoint timeline, Savitar would find his way out of the Speed Force prison and haunt Barry Allen throughout Season 3. The timeline was later erased out of existence when H.R. Wells disguised himself as Iris. Savitar killed H.R. instead of Iris and thus Barry never had to create the time remnants to defeat Savitar.
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The Nora Allen Timeline
Season 5 of The Flash brought in another alternate future timeline which Barry Allen and Iris West’s daughter Nora Allen belonged to. The fifth season of the Flash revolved around the dynamics of Barry Allen, Iris West, and Nora West-Allen. Although many of the changes that happened could be attributed to Nora’s unruly actions, the majority of the pivotal timeline changes were Barry’s doing. He was the one who destroyed Cicada’s dagger. This threw a monkey wrench into Grace Gibbons’ plans of killing all the meta humans of Earth. This did help in stopping Cicada’s evil designs and Barry’s eventual disappearance in 2024. But what it also caused was the release of Eobard Thawne from his prison, destroying Nora Allen’s timeline. The effects of his actions reached far and wide. The multiverse spanning Crisis event, which ended up getting preponed from 2024 to 209, was mostly because of the Nora Allen timeline’s repercussions. The Earth 90 Barry Allen was doomed because Barry Allen could no longer keep it in his pants. Good going Flash!!
The Flashpoint Timeline
The most important and genre-defining event in the history of the Arrowverse, Flashpoint did not just affect The Flash.. The consequences of Barry’s actions rippled across the universe. Even Arrow felt it. It also invited the wrath of the Dominators, who were angry with the Flash meddling with time. The Flash loses his father to Zoom. Now an orphan, he travels back in time in Episode 23 of Season 2 in “The Race of His Life”. Barry stops Reverse Flash from killing Nora Allen. He imprisons Thawne so that he could never manipulate Barry’s life again. In the Flashpoint timeline, Both of Barry’s parents are alive. Cisco has now taken over Star Labs, his company now called Ramon industries. Wally West was the new Flash. After the Rival badly injures Wally, Thawne convinces Barry to let him go. The act of restoring the timeline meant Barry would have to allow Reverse Flash to run back in time and kill Barry’s mother. Flashpoint will forever be the most important timeline change in the history of the Arrowverse.