[SPOILERS for those not caught up on The Flash ahead.]
The character Ronnie Raymond (Robbie Amell) has had a tough road of self-sacrifice on The Flash. In season one, the S.T.A.R. labs engineer worked to minimize the fatalities from the particle accelerator accident and was trapped in the explosion himself. Initially presumed dead, Ronnie had actually merged with Dr. Martin Stein (Victor Garber) into powerful metahuman Firestorm.
Though eventually separated and allowed to briefly unite with his fiancee Caitlin Snow (Danielle Panabaker), Ronnie plunged into danger once again in season 2. A Firestorm separation was strong enough to save the city from the unstable singularity created by The Flash's (Grant Gustin) trip back in time, but only Stein made it out when the wormhole collapsed.
That singularity has been the gift that keeps on giving, opening up a bridge between realities. That connection has brought Team Flash both new friends and enemies from the alternate world of Earth 2, as well as another enigmatic Dr. Harrison Wells (Tom Cavanagh). Now we have confirmation that the team will be challenged by another familiar face.
A recent leaked set photo of actor Robbie Amell showed him in a different costume than his usual Firestorm look, leading to speculation that Earth 2 would provide us with an alternate version of Ronnie. Now EW has confirmed that speculation, with the added spin that Earth 2 Ronnie has transformed into villain Deathstorm. He's also still together with his version of Caitlin, a.k.a. Killer Frost.
Here is the official statement on the matter from The Flash executive producer Andrew Kreisberg:
“We are beyond excited to have Robbie back on The Flash. You can’t keep a good Firestorm down. Only this time, he’s back with a twist, a deadly Earth-Two version of our beloved Ronnie in the form of Deathstorm.”
In the comic universe, Firestorm is resurrected as Deathstorm (along with many other heroes and villains) to become an unwilling part of the deadly Black Lantern Corps. Deathstorm has a complicated history of merges and separations, and the same universe-destroying volatility as we've seen with Firestorm.
Killer Frost has a few different versions in the comics, though the most recent was an alter ego of Caitlin. Her ability to transfer heat into cold means, contrary to the usual overpowering effects of fire on ice, Killer Frost actually grows stronger from the flames. This explains how her opposites-attract relationship with Deathstorm on The Flash would work to her advantage. As The Flash has frequently played around with the storylines of well-known comic characters, it's likely Deathstorm will be based less on undead armies and more on a symbiotic relationship with Killer Frost.
The appearance of Ronnie once again in Earth 1's universe will also provide more emotional drama for Team Flash, especially Caitlin. If anyone has a reason to turn into a super villain herself, the constant see-saw of love and loss in Caitlin's life makes her a prime candidate. It will be interesting to see how she reacts to an alternate version of her story - one that contains less loss but more evil intentions.
The Flash will return on Tuesday, January 19, 2016 at 8pm on The CW, while Arrow will return on Wednesday, January 20, 2016 at 8pm on The CW and Legends of Tomorrow will see its series premiere on Thursday, January 21, 2016 at 8pm on The CW.