One of the defining features of 2020's Watch Dogs Legion is that you're able to take control of basically anyone in the game's version of London. Associate producer Shelley Johnson said in a new interview that the technical underpinnings of Legion are "complex almost beyond description."

"This is probably one of the most ambitious games Ubi has ever imagined," Johnson told Stevivor. "It was certainly from a management standpoint and a creative standpoint, the biggest challenge yet, certainly for me personally."

Johnson told Gamecrate earlier this year that there is no limit to the number of different NPCs that players can assume control of in Legion. "One of the numbers that was floating around at one point was 9 million," she said. "They're procedurally generated characters. So we've spent four years building the technology to be able to deliver on this promise and that includes the ability to piece together this huge city of characters as far as animation, dialogue, census data, like all those bio pieces that you see when you profile somebody, faces, character kids, all of this comes together to produce a unique character every time."

Johnson told Stevivor that it was an expensive, time-consuming process to make Legion a reality as it relates to the ambition under the hood. "[To] play as anyone, as a pillar--to really fulfil on the promise of that--it's expensive," she said. "This game is, in as far as challenge is concerned, complex almost beyond description."

Testing a game like Legion sounds like a big challenge, and Johnson said it's the first game from Ubisoft that reached the limits of what human testing was capable of. She added that, in the future, games with the complexity and scale of Legion may need to make use of AI to pick up "some of the heavy lifting."

Watch Dogs Legion launches in March 2020 for PS4, Xbox One, and PC. Check out the video embedded above to learn more.