The Flash season 6, despite ending early, has its villain break a long-lasting season finale tradition that has been consistent in the past five seasons. Since the Grant Gustin-led drama began its run in 2014, there has been a status quo that has remained unchanged when it comes to the the main villains; From evil speedsters to various dangerous metahumans, the fundamental structure never wavered from the villain losing in the end. The same can be said for most of the other Arrowverse shows.
With such a big number of episodes to run between October and May of every TV season, the shows have always had to follow a number of patterns before the heroes can defeat their respective main villain. While the seasons have also allowed for standalone stories to take the spotlight, the main begins to wrap-up around the final 3-5 episodes of the season. In the case of The Flash, Barry and the team will usually be knocked down over and over before they get to the finale where, eventually, their main foe gets defeated. What normally happens within the two final episodes of the season is a final confrontation before Barry defeats his antagonist.
When it came to Reverse-Flash, he was erased from existence after Eddie Thawne shot himself so that Eobard would never be born in the future. Other big baddies such as Zoom, Savitar, Thinker, and the Cicadas have all been defeated by the time their seasons were over, leaving Team Flash victorious. However, in the Flash season 6 finale, Eva McCulloch aka Mirror Mistress stood victorious over Team Flash. After having been determined to kill her husband, the Mirror Mistress succeeded in killing Carver despite his efforts in stopping her with his Black Hole syndicate. Barry, growing weaker without the Speed Force, couldn’t stop Eva from killing Carver, but Eva’s victory went beyond that. Not only does she get away with killing her husband and framing Sue Dearbon for his murder, but Eva also re-enters society as she takes control of the narrative.
Convincing the public that she had been kidnapped for years and that Carver died trying to save her after being briefly reunited, with Sue now wanted as his killer. Set to resume as the CEO of McCulloch Technologies, the season finale had the latest big bad stand victorious as Team Flash lost big time. While this ending wasn’t envisioned as the conclusion to The Flash season 6, breaking the tradition was still refreshing nonetheless. Eva has proven to be one of the show’s stronger and more uniquely complex characters since her introduction as she doesn’t come off entirely like a traditional villain. While taking someone’s life definitely makes her a criminal, there’s an anti-hero layer to her character.
With Barry and Eva both determined to stop Carver, it becomes all about their approach to it. One wants to see Carver go to jail while the other deems him unworthy to live. Since The Flash season 7 won't air until January 2021, it remains to be seen what Eva’s ultimate fate will be before the show begins its real season 7 story. But either way, to have a season end with a villain like Eva win over the heroes, made the season finale as strong as it was. Since Iris is still trapped in the Mirrorverse, that’s another aspect that puts Eva in the villain category that The Flash season 7 will have to explore when it returns to The CW next year.