This week is a huge one for Supergirl, The Flash, Arrow and Legends of Tomorrow — as they face a Crisis on Earth-X in a special two-night crossover event spanning the four series. As the title suggests, this collection of superheroes will have their work cut out as they try to thwart the nefarious machinations of the occupants of Earth-X. The use of alternate earths has been a mainstay in comics for a long time now. Indeed, Supergirl is actually set on a different version of earth to both The Flash, Arrow and Legends Of Tomorrow, but she is still able...read more