Heroes Join Forces

"Heroes Join Forces" is the second annual crossover event in the Arrowverse between The Flash and Arrow. It also served as a set-up for DC's Legends of Tomorrow by introducing characters who would be featured in that series. The crossover aired over two nights from December 1 to December 2, 2015. The episodes involved in the crossover were:


 * "Legends of Today" (The Flash)
 * "Legends of Yesterday" (Arrow)