Legends of Today

"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.

Synopsis
Vandal Savage arrives in Central City and sets his sights on Kendra Saunders. After Vandal attacks Kendra and Cisco, they turn to Barry for help. Realizing how dangerous Vandal is, Barry takes Kendra to Star City and asks Oliver and team to hide her until he can figure out how to stop Vandal. However, things quickly go from bad to worse when a man with wings AKA Hawkman shows up and flies off with Kendra. Meanwhile, Harrison develops a serum to make Barry run faster and asks Jay to test it out.

Trivia

 * When Vandal Savage is introduced, he is descending from the SS Tithonus. In Greek mythology, Tithonus was a Trojan who was granted immortality, but not everlasting youth.
 * This marks the first appearance of Thea Queen and Malcolm Merlyn on a Flash episode.