According to Sucker Punch co-founder Brian Fleming, the most difficult feature to implement in Ghost of Tsushima “hands-down” was combat. Fleming went into detail about how perfecting this key component was a six-year-long journey for the team that was absolutely crucial to get right.Fleming appeared at the GDC Showcase this week for a virtual Ask Me Anything (AKA) session to talk about the studio’s hit game Ghost of Tsushima. Fleming was asked early on in the session which feature was the most difficult for Sucker Punch to implement, to which Fleming responded without hesitation that it was combat.

“Easy answer and the answer is combat. The combat system was something that the team that worked on that — the handful of programmers and designers and animators — you know they worked nonstop for six years and built multiple versions of it with multiple approaches.”

In Ghost of Tsushima, players control Jin who starts out as a samurai but over the course of the game learns to fight using stealth. Ghost of Tsushima’s combat reflects this by incorporating both stealth combat and a unique sword dual system for more aggressive and straightforward combat.

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Fleming says combat, along with travel, was such a central aspect of Ghost of Tsushima that implementing a system that worked with Tsushima’s vast open-world while still being challenging and unique, was a constant challenge for the developers.

“The combat system along with a few other systems… they’re kind of the center of everything,” says Fleming. “They have to work in every situation, they have to work in every lighting situation, they have to work in every terrain, they have to work in every strange mode the game might be in — combat could potentially break out in.”

This also meant that there was no room to cheat the system, as some developers may have to as a natural part of game development (just look at how developers struggle with doors.) “It was an elusive, nonstop effort over literally a six-year journey continuing to work on that. I think the results were good but it was a long, difficult road.”

Fleming shared some other stories about Ghost of Tsushima’s development, including working with PlayStation’s Shuhei Yoshida to get the authenticity of the setting right, and how the seamless load times were a result of good programming and data management.

The virtual GDC Showcase will continue all week with more talks from developers behind games like Demon’s Souls and Spider-Man, so stay tuned for more news from IGN.

Matt T.M. Kim is IGN’s News Editor.