The Flash officially exists in a post-"Crisis on Infinite Earths" world, and that's bringing about some major new developments for the long-running Arrowverse series. Fans got to see exactly what that entailed in Tuesday's midseason premiere episode, which struck a balance between navigating the post-"Crisis" world and expanding upon a season-long mystery. In the process, the series teased a pretty noteworthy character for the episodes that are to come -- and left fans guessing with its cliffhanger ending. Spoilers for this week's episode of The Flash, "Marathon" below! Only look if you want to know!