"Legends of Today" is the eighth episode of the second season of The Flash and the thirty-first episode overall. It aired on December 1, 2015. The episode is the first part of a two-part crossover with the eighth episode of season four of Arrow. It acts as a setup for the series DC's Legends of Tomorrow, with the episode even introducing Vandal Savage, who is the "big bad" of the series' first season.