Supergirl: Medusa Season 2, Ep 8
Eliza comes to town for Thanksgiving, which seems like the perfect opportunity for Alex to come out to her mother. Meanwhile, Winn and James consider telling Kara the truth about the Guardian; and Kara wants to team up with Lena Luthor to combat a deadly virus unleashed by CADMUS. Finally, the Flash and Cisco arrive to ask Supergirl to come to their Earth to start the big 4-show crossover event.
Supergirl: World's Finest Season 1, Ep 18
The Flash comes from an alternate universe and aids Kara in her battle against Silver Banshee and Livewire in exchange for her help getting home.
The Flash: Legends of Today (Part 1) Season 2, Ep 8
In the first episode of a two-part crossover that will conclude in the next episode of Arrow, Vandal Savage arrives in Central City and sets his sights on Kendra Saunders. [more inside]
The Flash: Who Is Harrison Wells? Season 1, Ep 19
Joe and Cisco head to Starling City to continue their investigation of Dr. Wells. While in town, the duo enlists the help of Captain Lance, and Cisco meets the Black Canary, who asks him for a favor. Meanwhile, back in Central City, Barry races to catch a meta-human named Hannibal Bates who can transform himself into every person he touches – which includes Eddie, Iris, Caitlin and even The Flash.
The Flash: All-Star Team Up Season 1, Ep 18
Barry is surprised when Felicity Smoak arrives from Starling City along with her boyfriend, Ray Palmer, who flies in as the Atom. They've come to visit S.T.A.R. Labs as Ray needs help with his suit. Their timing turns out to be fortuitous because it’s all hands on deck after a meta human named Brie Larvin unleashes hundreds of robotic bees to attack and kill her former co-workers, including Dr. Tina McGee. A group dinner with Barry, Felicity, Ray, Iris and Eddie turns into a disaster.
Arrow: The Brave and the Bold Season 3, Ep 8
Part 2 of the Flash/Arrow crossover. Part 1 is The Flash: Flash vs. Arrow, in which Oliver & the team visited the Flash to ask for S.T.A.R. Labs' assistance in analyzing a boomerang used as a murder weapon. Now, back in Starling City, tracking the boomerang winds up putting Arrow into the middle of an A.R.G.U.S. operation. [more inside]