The second episode -- and first full installment -- of The CW's ambitious four-part crossover aired tonight, as the super friends assembled on "The Flash." Barry recruited Supergirl herself, as well as some familiar faces from "Arrow" and "DC's Legends of Tomorro,w" to fight an invading race of aliens called The Dominators. Part Three will continue tomorrow night on the 100th episode of "Arrow."

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The latest crossover promo shows the team on board the Dominator's ship, where Oliver will be caught in a dream state and shown the life he could have lived if he never became the Arrow. The promo features an engaged Oliver and Laurel Lance (the returning Katie Cassidy), the return of Deathstroke, and a revived iteration of Oliver's long-dead father, Robert Queen.

ARROW CELEBRATES 100 EPISODES; THE EPIC SUPERHERO CROSSOVER CONTINUES — Oliver (Stephen Amell) wakes up to a life where he never got on The Queen’s Gambit. Robert (guest star Jamey Sheridan) and Moira Queen (guest star Susanna Thompson) are alive and well. Laurel (guest star Katie Cassidy) is his loving fiancée and their wedding is imminent. Everything seems perfect, but Oliver starts to notice small imperfections that make him question this new reality. Meanwhile, Felicity (Emily Bett Rickards) and the recruits take on a new threat with help from The Flash (guest star Grant Gustin) and Supergirl (guest star Melissa Benoist). James Bamford directed the episode with story by Greg Berlanti and written by Marc Guggenheim & Wendy Mericle.

Starring Stephen Amell as the Emerald Archer, "Arrow" airs Wednesdays at 8 pm ET/PT on The CW. The series also stars Emily Bett Rickards, David Ramsey, John Barrowman, Willa Holland and more.