Part of the upcoming Assassin's Creed movie was shot in the Spanish town of Almeria in the Tabernas Desert. It's where famous westerns like The Good, The Bad, and The Ugly and Once Upon a Time in the West were shot, and some of the buildings, including a saloon, are still standing. As a treat for the cast and crew, Assassin's Creed star Michael Fassbender rented the town for a day of paintball.

"I thought as a treat I'd book the town and have a paintball shootout," Fassbender recalled during an appearance on The Tonight Show. "We used the saloon as HQ. They have real alcohol in there. Booze and paintballing, probably not a good idea."

Fassbender went on to discuss how he got shot at close range by a custom paintball gun, not a rental weapon like the one he was using. Here's how it went down:

"There are rules: you're not supposed to shoot somebody point-blank, but whatever. In the heat of the moment, battle is battle," Fassbender said. "The rental that I had, it got jammed, so I was like trying to push the balls through. And just as I just got it loaded up and fixed, I raised my head up--the guy came around the corner and he went [makes paintball gun noises] and [the paintballs] went right up my face."

"I had [what looked like] hickeys all the way up my neck and I was bleeding from the forehead," he said, referencing the welts that paintballs can leave on your skin.

In another segment, Fassbender and The Tonight Show host Jimmy Fallon had an air guitar battle. Check out the silly clip below, in which Fassbender rocks out to Ozzy Osbourne's "Crazy Train" and other songs.

Assassin's Creed opens on December 21. In addition to Fassbender, the film stars Marion Cotillard, Michael Kenneth Williams, Brendan Gleeson, and Jeremy Irons. It was directed by Justin Kurzel, who directed Fassbender and Cotillard in Macbeth.

Earlier this week, Ubisoft's Azaïzia Aymar made the bold prediction that Assassin's Creed will buck the trend of video game movies being mediocre or worse.

"I really think it's going to be a milestone movie," he said. "It's going to be the very first time that a video game studio creative works with movie creatives altogether to share a vision and give them the tool to express themselves; rather than have an adaptation. There's going to be a 'before and after Assassin's Creed movie' for sure."