In season 2, when Prof. Wells was trying to recreate conditions of a particle accelerator explosion to restore Flash’s powers, accidently Wally and Jesse got exposed to the dark matter radiation. But they didn’t immediately become a speedster, which puzzled all of us. It was only a matter of time before someone is transformed into a speedster, we saw Jesse Quick as the speedster fighting alongside Barry in the new timeline. In DC comics, he was born to Rudolf and Mary West. He was always looked down upon by his parents, bullied by his brother. He is the successor to Barry Allen. He was given Flash costume by Barry, who trained him and took him under his wing as “Kid Flash”, very soon Wally West will regain his speed powers in the present timeline as well.
Caitlin Snow took some time off to meet her mother with whom she has “issues”, she told her about her gradual transition into Killer Frost. She assessed that if she uses her powers more, the process will only speed up. Kevin Smith, a popular director who directed an episode of the Flash, is shooting another episode for the third season. He tweeted an image which revealed the title of the episode – Killer Frost. This triggered a speculation that Earth-2 doppelganger of Caitlin Snow/Danielle Panabaker would return to the show. But how can she come back ever if she is dead? The fans speculated that she could be another Killer Frost in a multi-verse (maybe from Earth-3).
So, what is the difference between Wally West turning into Kid Flash and Caitlin Snow becoming Killer Frost? In the post-flashpoint timeline, Wally is like a regular guy but would start to have visions of a previous life of a speedster just like Edward Clariss or ‘the Rival’. He will meet Dr. Alchemy who will offer him to regain his speed powers and he will accept it. Caitlin Snow was an ophthalmologist in the previous timeline, but in the current timeline she got struck by particle accelerator explosion and is now turning into Killer Frost.