Assassin’s Creed is set in a world that will feel familiar to fans of the video game franchise, but its characters and artifacts are all new.

During a visit to the set of the 20th Century Fox film, the creative team behind the movie explained the decision to start from scratch with their mythology.

“We essentially did them all on our own because we wanted to have an original script,” said executive producer Pat Crowley. “It’s a movie that’s based on the game, but it’s not a movie that is the game.”

Director Justin Kurzel explained that the decision to differentiate the characters and storylines was because the Assassin’s Creed games already have so much backstory for each of their characters. Since those had already been mined, he wanted to offer viewers something new.

“It was about trying to inject a new character who can have some sort of relationship with the game perhaps in the future. It was essentially about finding a character that was fresh,” Kurzel said. “It’s an origin story too. It’s about a man that doesn’t realize he’s an Assassin in the present day and discovers that and discovers skills and discovers an identity and discovers that he’s part of a tribe. That became the real focus that we concentrated on. We needed, especially in the present day, a character that enabled us to do that.”

To make sure their new storyline stayed true to the Assassin’s Creed franchise, Crowley and Kurzel worked closely with Ubisoft. They used Ubisoft’s encyclopedia of Assassin’s Creed rules, which included details like how much of an ancestor’s memories you can access and how you can’t change the past, to set up the framework of the script. Ubisoft ambassadors also would come to set to offer their approval.

“[The movie] exists within the rules and the world that Ubisoft has set up that Assassin’s Creed can take place in,” said Crowley. “We just went ahead and created a new [story] that respected the rules, that a gamer could come and go, ‘I know this world.’”

Even though the characters aren’t the same, there will be a handful of nods to previous Assassin’s Creed figures from the game scattered throughout the film. Armorer Tim Wildgoose was a huge fan of the Assassin’s Creed games when he signed on to make the movie’s weapons, and because of that he littered Easter eggs throughout various sets.

“Justin basically said to me, because I know the games very well, ‘Pick whatever you think would be iconic,’” said Wildgoose. “That also means I get to choose my favorite weapons and make them for real.”

Though 80% of the weapons were created from new (and, according to Wildgoose, many were inspired by real-life weapons in the Wallace Collection), expect to see the Guillotine Gun from Assassin’s Creed Unity, Connor’s bow from Assassin’s Creed III, Baptiste’s sword from Assassin’s Creed III: Liberation, Shao Jun’s sword from Assassin’s Creed Chronicles: China and more if you keep your eyes peeled.

“We’re just going to have it in the background somewhere so the fans can watch it and spot these things,” he said.

Production designer Andy Nichols also left nods to the games throughout the movie. Various uniforms, outfits, literature and engravings will be references to Assassin’s Creed games that eagle-eyed viewers can spot (though, here’s a hint: a lot of them are going to be in Abstergo CEO Alan Rikkin’s office).

The groundwork laid in this movie will be used going forward if Fox’s Assassin’s Creed movie becomes the trilogy it’s intended to be. On set, star and producer Michael Fassbender said that work had already begun on a second movie, and they have the idea for what a third will be as well.

“It’s not a one-off,” said Crowley. “Everybody expects that this movie will continue.”

Assassin’s Creed hits theaters on December 21, 2016.