"Arrow" season 6 episode 8 aired much earlier than expected due to the Arrowverse crossover event with other The CW superhero shows. It includes "Supergirl," "The Flash," and "Legends of Tomorrow."

After dealing with desperate circumstances in the previous episode, the "Arrow" protagonist will find himself battling against the Nazis in episode 8. The crossover, titled "Crisis on Earth X," started on Nov. 27 with episodes from both "Supergirl" season 3 and "Arrow" season 6.

Promotional photos for the episodes reveal that Oliver Queen and Felicity Smoak (Emily Bett Rickards) will head to Central City to attend Barry Allen and Iris West's wedding ceremony. However, fans expect that this will not be a peaceful wedding, The trailer for episode 8 suggests that the ceremony will be plagued with trouble.

The villains in the upcoming crossover are from Earth X, an alternate world wherein the Nazis won the Second World War. Earth X versions of the superheroes come to invade as their villainous counterparts, featuring Dark Arrow, Overgirl, and Dark Flash.

Stephen Amell, who plays Green Arrow, believes that the upcoming episode is not the usual crossover from The CW. In an interview with TV Line, he said, "Call it the crossover if you want. But it's kind of like calling the Super Bowl just a football game."

The crossover will continue in "Legends of Tomorrow," with characters Sara Lance (Caity Lotz) and Dr. Martin (Victor Garber) in the spotlight. Fans can also expect the appearance of Alex Danvers (Chyler Leigh), Citizen Cold (Wentworth Miller), and The Ray (Russell Tovey).

Lotz herself expressed her praise for the crossover event, saying it was better than last year.

The crossover kicked off with "Supergirl" which aired on Nov. 27, 8 p.m. Eastern Standard Time (EST). It was followed by "Arrow" at 9 p.m. EST. Following these are parts three and four on "The Flash" and "Legends of Tomorrow," expected to air on Dec. 29.