Thanks to TVLINE, we have a pretty big clue as to who will be the supervillain antagonist of the second episode of The CW's Flash.
Q:What can you tell me about Stephen Amell’s cameo in the pilot for The Flash?
TVLINE: I can tell you that it’s a nice enough, if obvious, moment, where Barry seeks out the nudge he needs to be the hero he now can be. Now, if I can interest you in some Episode 2 scoop, I am hearing that the second metahuman The Flash will face off against might make us all feel a bit… well, Mist-y.
The most obvious choice, is that the second episode of the Flash series will feature a metahuman villain named the Mist. And true enough, there's is a DC Comics villain that goes by that moniker. The Mist is an obscure villain from the 1990's Starman series. Johnathon Smythe, was a scientist and war hero who invented a "device that turned his body into a gaseous form" and subsequently went on a crimewave in Opal City. Over the years, the character has also passed down the mantle of Mist to his children, who went by the alter-egos of Kyle Nimbus and Nash Nimbus. Of course, this is just my own guess based on the clue from TVLINE. There's also Mist Master, Dr. Mist, and a couple more possibilities and characters in play as well. Feel free to make your own guesses in the comment section below.
Johnathon Smythe as The Mist
Nash Nimbus as The Mist