Major spoilers below for the latest episode of The Flash.
While "Therefore She Is" delivered a wealth of new and extremely interesting information about Marlize DeVoe and her husband's horrifying plans for the Enlightenment, the final few seconds were perhaps the most exciting, as they proved true fans' theories that Jessica Parker Kennedy's Mystery Girl is indeed a speedster within this universe. Not that we know where she came from, or even when she came from. But that split-second reveal may have shown us that not only does Mystery Girl share Barry's meta-abilities, but she could actually be more powerful than the so-called Fastest Man Alive.
That line of speculation wasn't just randomly generated, but is rather inspired by how Mystery Girl's powers were visually represented: with a previously unseen combination of yellow and purple lightning. As fans of both The Flash TV show and the comics are aware, the color of a speedster's lightning offers unique classification insight. The live-action series still hasn't provided all the information needed on that front, particularly when it comes to the purple lightning, but Mystery Girl herself may provide some needed explanations.
Generally speaking, yellowish lightning represents a pure connection to the Speed Force, so the fact that she sports it is almost definitely tethered to the weird symbols that both Barry and Mystery Girl have jotted down throughout the season. As well, yellow is basically the starter color for speedsters, and it was the color of Barry's electrified wake when the series first started, as well as those of Wally, Jesse and others just getting used to their powers. As those powers get stronger, the lightning's shade turns more orange, such as where Barry's is now. And Mystery Girl's lightning color was indeed more fiery than, say, lemony, so she's definitely not just testing her powers out for the first times. But could she be faster than Barry?
On the flip side, The Flash has only shown us speedsters with purple lightning twice so far. The first was in Season 3, when viewers were introduced to Accelerated Man, Earth-19's stand-in for The Flash, and the second happened when Iris temporarily gained super-speed. As of yet, the TV show has yet to explain what the specific distinction is with purple lightning. It has shown us that blue lightning is the result of using the Velocity formula, with deep red indicating a negatively corrupted connection to the Speed Force, so it's possible, as a rough combination of the two, that purple lightning signifies a weaker connection to the Speed Force. But that would be antithetical to the yellow one, so I'm just in the dark here.
Still, Mystery Girl is the first character to show off dual lightning hues, which probably means she's working with a different set of speedster genetics than we're used to seeing. The most obvious presumption is that she's a combination of Barry's yellow and Iris' purple as the live-action iteration of the couple's quick-footed daughter Dawn Allen. And if that's the case, or even if she's the offspring of two other speed-powered entities in the Arrow-verse, it stands to reason that Mystery Girl could and would be more powerful than someone who doesn't have speedsters in their family history. And considering she has slipped into the protagonists' lives as easily as she pleases, Barry had better hope she continues dropping off gifts instead of threats.
Because even though she has put on a polite and good-natured face to each of the Team Flash members she's met before, Mystery Girl has shown viewers a much different face when she's alone. It's not necessarily an evil look, but gives off a "sick of all this" vibe, meaning even if she's not a villain, she could be in a situation where she's forced into doing someone else's villainous tasks. (Such as The Thinker's.) She looks like she's engaging in some devious time-meddling chicanery with each of her appearances, and we know the character is a major factor in setting up Season 5, so for Barry and Iris' sake, may the yellow-and-purple lightning's true meaning be one of love and keeping Central City safe.
With just three episodes left in Season 4, The Flash brings the confusion to The CW every Tuesday night at 8:00 p.m. ET. Check out our TV finale rundown to see when your favorite shows are ending soon, and to learn what new and returning shows will pop up when the Scarlet Speedster is on hiatus, head to our summer premiere schedule.