A surprising alliance will happen to stop Damien Darhk in the upcoming finale episode, titled "Schism," of the fourth season of the superhero series "Arrow."

Oliver decides to team up with an unexpected force in order to put an end to Damien Darhk's powers. Darhk's secret plans involved nuclear Armageddon to wipe out the humans and start anew.

The promo trailer for "Schism" shows Darhk challenging Team Arrow in a battle that could involve Star City. Darhk reveals that he wants to "cleanse" humanity by doing a mercy killing in a global scale. Arrow promises to the people that they will put a stop to Darhk's plans.

In an interview with Entertainment Weekly, Oliver's Stephen Amell shared what fans can expect from the last episode of the season. "I can tease that there is an ultimate showdown, and that ultimate showdown takes place on a level playing field," he said. "And I know the hook from the last episode made it feel like the whole episode would be about rescuing Felicity, and that's really not the case at all. We solve that problem pretty early on."

Amell also added that there will be resolution to Oliver, Darhk, and also to the majority of the core characters."Schism" will also introduce a villain that fans can learn more in the next season.

As for Oliver and Felicity, the actor said, "Last year, the team was staying, Oliver and Felicity were going. In this finale, it feels very similar because it's almost the opposite."

Meanwhile, the previous episode, titled "Lost in the Flood," saw Darhk's attempt to reactivate "Rubicon" with the help of Cooper. He also launched the remaining missiles. Fortunately, Team Arrow was successful in stopping the "Rubicon" for good. Oliver and Diggle, on the other hand, searched an underground town to search for Thea. Apparently, Malcolm drugged her to make her turn against her own brother, Oliver.

"Arrow" season 4 finale airs tonight at 8 p.m. on The CW.