WARNING: The following article contains spoilers for The Flash Season 6, Episode 15, "The Exorcism of Nash Wells."
Ever since the end of the "Crisis on Infinite Earths" crossover, Nash Wells has been experiencing visions of alternate versions of Harrison Wells. It started off as merely a nuisance when someone such as Harry Wells showed up, but it eventually turned into a massive problem when Eobard Thawne revealed himself as one of the alternate versions of Wells living in Nash's head. Things only grew worse from there in "The Exorcism of Nash Wells," as the Reverse-Flash attempted to take over Nash's body.
Thankfully, Cisco and the team came up with a solution to save Nash and exorcise Eobard from his body for good. Yet, while they were successful, they may have also inadvertently made the Reverse-Flash more dangerous than he has ever been before.
In The Flash's latest episode, Eobard Thawne threatened to make a full-blown comeback. After the new Earth-Prime was created in "Crisis on Infinite Earths," all versions of Harrison Wells converged into Nash's head, and Thawne was on the verge of taking over his body permanently. In fact, even his super-speed powers were coming back with him, and Team Flash couldn't risk their ultimate nemesis staging a return.
Therefore, they devised a plan to exorcise Thawne from Nash. The process is technical and complicated and not without its hiccups, but eventually, the team is successful at ridding Nash of the supervillain. Yet, there is also an unfortunate consequence. When Thawne leaves Nash's body, it's in the form of a massive, red lightning storm that reaches out into the sky.
This indicates the energy of Eobard Thawne has been released into the atmosphere, meaning that now, the supervillain is formless but still somewhere out there in the world. It may take him some time, but he will most assuredly find a way to possess someone else -- that is, if he somehow doesn't figure out how to put himself back together without a "host" body.
Either way, by saving Nash Wells, Team Flash has just helped make their worst enemy even more dangerous than he used to be. Right now, he is out there without a body, but he could come back looking like anyone -- maybe even someone who can get close to them. Since that is exactly what Thawne did the first time around all the way back in Season 1 when he first took Harrison Wells' face, this is definitely something he could do again. After all, the Reverse-Flash loves his tricks.
Airing Tuesdays at 8 p.m. ET/PT on The CW, The Flash stars Grant Gustin, Candice Patton, Carlos Valdes, Danielle Panabaker, Tom Cavanagh, Jesse L. Martin, Danielle Nicolet and Hartley Sawyer.