Everything Oliver and crew have gone through in Season Three has been building up to this.

Ever since Sara Lance's murder, Team Arrow has been pushed to the limit. Laurel assumed the Black Canary mantle; Thea died, and was resurrected; Roy left; Oliver's secret identity was blown, leading him to reluctantly become the leader of the League of Assassins. Now, in order to save Starling City, Oliver must once again face Ra's al Ghul, the foe who previously bested him in combat and left him for dead. More than that, Oliver must somehow find a way to survive.

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Ahead of tonight's "Arrow" finale, executive producer Marc Guggenheim spoke with CBR about what it will take to defeat Ra's, Oliver's change in attitude, Thea's growth and involving the Flash in the series' season closer. Then, as if that weren't enough, Guggenheim opens up about Season Four and the new major threat it will pit against the defenders of Starling City.

CBR News: Oliver didn't stand a chance against Ra's al Ghul in their last encounter. What's different in Round Two? What can viewers expect from this confrontation?

Marc Guggenheim: Oliver is different. Episode 309, "The Climb," was the last time Oliver fought Ra's. It was almost a lifetime ago. The question I think you are asking is definitely answered in the finale. We've always said this season has to do with identity. Given the theme, it's appropriate that the key to Oliver defeating Ra's lies in identity.

It's hard to figure out Malcolm Merlyn [John Barrowman]. Is he a double double agent? Where do his loyalties lie?

The finale will also definitively answer that question. You'll not only get an answer to that question, but really get a good sense as to what's been motivating him. I think pretty much all his recent actions will get explained.

How conflicted is Nyssa on which side to stand?

I don't think she's that conflicted. Once Ra's forced her to marry Oliver, once they had their scenes in episode 322, any level of conflict went away. This episode you get a very clear sense as to where Nyssa stands with her father and what her feelings are towards him.

Thea [Willa Holland] has been manipulated, killed, resurrected and forced to watch her brother become the next Ra's in order to keep her safe. How have all these events shaped her?

She's been on a season-long journey. It's not just about her near-death experience or her resurrection. It really was about the whole year for her. The training she got from Malcolm, the brainwashing, the discovery of the brainwashing, the ups-and-downs about her relationship with Malcolm -- all of these things are very much in part of the journey she's been going on all year long. This season finale is, I wouldn't say the end to her story -- it's just the culmination in terms of everything she's gone through, as well as the ups-and-downs that she's had vis-a-vis her relationship with Malcolm. Both those plotlines get a pretty definitive answer in this episode, while still setting her up for where we're planning on taking her character next year.

There are still a lot of players on the board. Tatsu, Detective Lance, Diggle, Laure, Felicity -- where do they fit into the finale?

Everyone has a role to play. Lance and Laurel's critical thing is their relationship. We're not going to put a tidy bow on their relationship. I don't think that would be realistic in light of everything that has happened between these two characters. At the same time, we're evolving their relationship past the point of Laurel saying, "I'm sorry," and Lance saying, "I'll never forgive you."

We basically leave Tatsu open and available to us in Season Four. There was a lot of talk in the writers' room about how involved she should be in the finale. At the end of the day, you only have 42 minutes. We had an organic place to leave her, and it felt like the right end to her storyline this year. But it also leaves open the door to return next year. Tatsu's screen time really comes in the flashbacks this episode. We still have to tell the conclusion of that story.

What was the thought process behind involving the Flash?

It's something that we had talked about ever since the beginning of the year. Basically, wouldn't it be fun to have the Flash be part of the finale? A finale, to me, is always like a celebration of the entire season. Certainly, the crossover with Flash was a high point for us. I always describe the finale -- when I'm trying to get agents to let their clients be on a finale of "Arrow" -- I always say it's like a party, and everyone is invited. That's as good a way as any to explain the reason for having Barry on the show. At the same time, his participation is not accidental. It's actually very pivotal. The whole episode couldn't happen if not for Barry. He plays a significant role.

Can you talk about the Felicity/Oliver/Ray triangle? Will there be some resolution?

I think you get a pretty definitive resolution. There's certainly a scene between Ray and Felicity. If it wasn't clear that things were over between them in episode 20, we hit the grace note on their relationship in 23.

Oliver made some tough decisions this season. How do you feel they've changed him?

The big thing for Oliver is that despite everything, he's actually started to care about people. Oliver's first inclination is always to go at it alone. This episode, in particular, teaches him that instinct hasn't served him well. It's cost him some relationships and jeopardized his life. It's true like the song says. "If people who need people are the happiest people in the world," then Oliver realizes he needs people.

Does the finale set the table for Season Four?

The finale isn't designed to set up Season Four. That said, there are a lot of elements of the finale that are being carried over to Season Four. There are certain relationship issues, and we will be teeing up Damien Darhk further in the season finale, which we've never done before, which is tee up the next year's season bad in the current season finale.

At the same time, it's a pretty conclusive end, not just to the season, but this episode could really function as a series finale, should people want it to. I hope they don't want it to.