Special Guest Stars Caity Lotz as Sara Lance Grant Gustin as Barry Allen Melissa Benoist as Supergirl Danielle Panabaker as Caitlin Snow Chyler Leigh as Alex Danvers Melissa Benoist as Kara Zor-El (Earth-X) / Overgirl Tom Cavanagh as Harrison Wells Tom Cavanagh as Eobard Thawne / Reverse-Flash Dominic Purcell as Mick Rory / Heat Wave Victor Garber as Martin Stein / Firestorm Colin Donnell as Tommy Merlyn (Earth-X) / Prometheus Candice Patton as Iris West Franz Drameh as Jefferson "Jax" Jackson / Firestorm Uncredited Stephen Amell as Oliver Queen (Earth-X) / Dark Arrow