The Flash's Danielle Panabaker Teases the Introduction of Killer Frost and Velocity 9. The Flash fans have been waiting patiently to meet Caitlin Snow's (Danielle Panabaker) villainous alter-ego Killer Frost. On Tuesday we'll finally get the honor, when Barry (Grant Gustin), Wells (Tom Cavanagh) and Cisco (Carlos Valdes) visit Earth-2.