Arrow is still a few weeks from wrapping up its sixth season, but even though there is still quite a bit to unpack before the season finale The CW series' showrunner says that finale will be a major game-changer.

Speaking with Entertainment Weekly, Marc Guggenheim -- who is showrunner for both Arrow and Legends of Tomorrow -- revealed that the upcoming Arrow season finale is going to be both unconventional and completely change things for the series.

"It's gonna be interesting," Guggenheim said. "It's very, you know, I've been saying it's an unconventional kind of finale. It still feels very much like a season finale. When I first started talking about it we hadn't written the darn thing yet, but now we've written it and we're in prep on it and on Monday we start shooting. And it's a real game-changer."

To a certain extent, the season five finale was also a game-changer for the show with Adrian Chase/Prometheus' (Josh Segarra) end game resulting in Lian Yiu being blown up, Oliver Queen/Green Arrow (Stephen Amell) becoming a single parent after the murder of his son's mother, as well as setting into motion some of the events this season -- Thea (Willa Holland) in a coma, Oliver trying to find a work-life-vigilante balance, and the splintering of Team Arrow. However, what's coming for the season six finale will go even further and Guggenheim teased that the aftermath of "Lian Yu" as seen in the season six premiere will play a role as they've been plotting up to this game-changer from premiere.

"The show fundamentally changes in the finale and I think you'll see there's stuff that we were seeding back in the season premiere that finally comes to fruition here in the season finale, so you'll see that there was a very specific plan to the entire season," Guggenheim said. "We always knew that this is where we were headed to. So, hopefully in subtle ways have been teasing this all along without you realizing it. My hope is that people are surprised, but also look back and are like oh, that was kind of the only way that they could have ended the season."

It's something that series star Stephen Amell has teased previously. Amell told fans at Heroes & Villains Fan Fest in Chicago last weekend that something happens going towards season seven that can't be undone -- even more than blowing up Lian Yu -- and Guggenheim confirmed that. He even went so far as to explain that the show isn't going to go back and correct whatever the big twist is. The game-changer will stand.

"That is, yes, that is exactly true," he said. "In fact, it's the kind of game-changer that we're not going to buy back at any point. It fundamentally changes the show."

As for what that fundamental change is, fans have theorized everything from a death to Oliver losing an arm -- a reference to the first season episode of Legends of Tomorrow "Star City 2046" where the heroes end up in a dystopian future that features an older, grittier version of Oliver Queen who just so happens to be missing an arm. However, the most popular thought is that Oliver will get his Iron Man moment by openly and publicly revealing his Green Arrow identity, a move that would be a game-changer for sure.

Arrow airs Thursdays at 9/8c on The CW.

What do you think will be the big game-changer in the season finale? Sound off with your theories in the comments!