The CW has unveiled the official trailer for "Flash vs. Arrow," next week's two-night crossover event of its two biggest shows as the heroes come together to stop a threat that could destroy Central City. You can see that trailer below. Producer Marc Guggenheim has also given some interviews about the episodes and revealed new details about the rest of the seasons for both shows. In a big surprise, the hardline rule of keeping things real world in "Arrow" and not including metahumans is being thrown out the window.