The Flash’s latest episode has Nora and Bart West-Allen accidentally change a major Central City milestone while trying to fix a mistake in the past.

WARNING: The following contains spoilers for The Flash Season 8, Episode 6, “Impulsive Excessive Disorder,” which aired Wednesday, March 9 on The CW.
The Flash’s shorter than usual Season 8 made its return with the Nora and Bart-centric episode “Impulsive Excessive Disorder,” which picked up right after the Season 7 finale. After helping Team Flash with the Godspeed War, Nora and Bart returned to 2049 to discover that their interference prevented Jay Garrick’s death. While this was good news at first, the young speedsters found out that Jay’s marriage to Joan also did not happen — so they needed to go back to the past in order to fix that mistake. However, while doing so, they inadvertently retconned Central City’s first meta-crime.
Using their understanding of the timeline, the West-Allen kids calculated that the change happened due to their grandfather Joe West (played by Jesse L. Martin, who recently dropped some Flash hints) being shot during a robbery back in 2013 while Barry was still in his nine-month coma following the particle accelerator explosion. Thinking this would be an easy fix, Bart used his super-speed to move his grandfather away from the bullet’s trajectory, ensuring Joe would survive the encounter unharmed. But Nora was furious with her brother; she was worried about the side effects caused by moving Joe instead of the bullet. She argued with Bart about his reckless behavior and was overheard by Mona Taylor a.k.a Queen, a founding member of the Royal Flush Gang.

Mona was under the assumption that she was the only one imbued with abilities, since the episode took place in 2013. It wasn’t until much later in the year — with the introduction of The Flash — that metahumans started to come out of the shadows to cause chaos in Central City. After Mona overheard the speedsters, she was relieved to find out there were other powered beings in the city. This news inspired her to rob a casino with help from King, Jake Fox and Wanda Wayland; the four metas would eventually become the Royal Flush Gang.
While the Royal Flush Gang would have eventually formed without the kids interfering with the timeline, that wouldn’t take place until a few years after the explosion and well after many other meta criminals escaped the shadows — specifically the very first meta criminal: Clyde Mardon a.k.a The Weather Wizard.

Mardon appeared in the pilot episode of The Flash, giving Central City its first taste of dangerous metahumans. Luckily, Barry was awake by that point and able to stop Mardon in his first outing as the Scarlet Speedster. From that moment on, many other metas tried their hand at using their abilities to commit crimes and challenge the new hero of Central City. But in the newly altered timeline with the Royal Flush Gang forming earlier on, Central City got introduced to metahumans many months before they knew there was a hero who would save them from such threats.
Nora and Bart were able to stop the Royal Flush Gang without anyone getting hurt or killed, leaving Central City safe long enough for Barry to wake up from his coma and take on Mardon as he had before. The kids got back to the future with Jay still alive, well and married to Joan (plus potentially heading for a spinoff). Their small retcon of Flash history, however, still stands meaning that some Central City citizens got an appetizer of metas before the weather-controlled main course of Clyde Mardon.