Fans, especially those who have read the DC comic books, always knew that The Flash ally Caitlin Snow will eventually turn into one of the supervillains Killer Frost. And the latest "The Flash" season 2 trailer says the inevitable is happening sooner than later. As if that's not trouble enough for Central City's resident speedster, an old foe is making a comeback.

A new "The Flash" season 2 trailer has been published on the Internet. YouTube account Telelvision Promos has posted the said video, "Everything Will Change," and the title does seem appropriate, especially as fans finally get to see the "bad" and very blonde Caitlin Snow a.k.a. Killer Frost (Danielle Panabaker).

Will the blonde have more fun this time out? Caitlin thinks so as she says, "It's so much more fun to be bad." 

That may prove to be difficult to handle for Barry Allen a.k.a. The Flash (Grant Gustin), as Caitlin is one of his bestfriends-slash-allies at S.T.A.R. Labs. But Killer Frost isn't the only one he has to face when The CW superhero television show returns.

The trailer also had Cisco Ramon (Carlos Valdes) declaring, "Reverse-Flash is back." In fact, viewers get a good glimpse of him in the trailer. Only this time, he does not look like Dr. Harrison Wells (Tom Cavanagh) but rather his original self, Eobard Thawne (Matt Letscher).

For those who might have forgotten,Reverse-Flash is really Eobard Thawne, who got stuck in the past when he tried to kill Barry's mother. So he suck up the real Dr. Harrison Well's DNA and pretended to be him up until the time he was wiped into existence in the season 1 finale.

So if he was wiped into existence, how come he's back? Well, that information is something fans will have to find out when the show returns in a few weeks' time.

But executive producer Todd Helbing did reveal this to Entertainment Weekly, "His impossible return to Central City puts a member of the S.T.A.R. Labs team in unexpected danger, forcing Barry to make a life-changing decision."

Find out all of these (plus get a glimpse of Earth-2 Barry Allen and Iris West) when "The Flash" season 2 returns with a new episode on The CW this Jan. 19, 8 p.m.