Emergent storytelling is one of the most powerful and unique tools in the game designer’s arsenal according to Nick Popovich, co-founder of the California-based studio Monomi Park.

Speaking at the Game Developer’s Conference in San Francisco this afternoon, Popovich, the creator of Slime Rancher, one of 2016’s hit independent games said that, by relinquishing a little control to the player, game designers are able to facilitate surprising and highly memorable in-game moments for players.

Popovich argued that emergent storytelling has long been the “secret sauce” in game development. He compared the original Halo: Combat Evolved, which was released in 2001, to 2007’s Call of Duty: Modern Warfare. Both games are foundational examples of the first-person shooter genre, and yet for Popovich, Halo is the more memorable game because it allows players freedom to manipulate the game’s systems in personal, creative ways. These moments, which occur within the systems that the designers have laid out, but which do not follow strict rails, are often the most memorable, and widely shared of all. “Emergent storytelling is linked to how much control the designer is willing to give up,” Popovich said, before adding: “A little goes a long way.”

In Slime Rancher players role-play as a rancher who relocates to a distant planet as an eponymous ‘slime rancher’, collecting, raising, feeding, and breeding slimes. Popovich explained that it was deceptively straightforward to add emergent storytelling to the game. The designers gave each breed of slime a different set of ‘wants’ and ‘needs’. “When these collide,” he said, “interesting and memorable things happen.” Popovich showed a YouTube video in which a player had herded slimes into a pen. On the other side of the pen two chickens, which slimes consider food, were loitering. In the video, the player expresses astonishment as the slimes appear to organise into a stack in the corner of the pen, using the ‘slime ladder’ to escape the pen to reach the chickens.

This vibrant, unpredictable behaviour was, Popovich said, crafted from surprisingly simple systems. The slimes automatically stack like Lego bricks when squished into a tight space. Likewise, they automatically try to move toward food sources. For the player, it appeared as though the slimes were self-organising. In fact, they were following a couple of simple, un-coordinated scripted behaviours. “Half of these things were just accidents, but the player imposes a story to what’s happening,” said Popovich.

“Only half of the story matters,” said Popovich. “These stories can be extremely short, and players don’t need to observe the entire emergent sequence to appreciate what’s happening. As they begin to learn the game’s systems, they’ll figure out how it all works when they finally observe all of the elements in the emergent chain reaction.”

Players are in on the joke when it comes to emergent storytelling, Popovich argued. “It may disrupt the experience, leading to player death, for example, but it rarely breaks immersion.” Popovich attempted to distinguish emergent behaviours from bugs, but pointed out that often the distinction is thin. He gave the example of a first-person shooter where an enemy soldier runs into a wall. In this instance the player perceives this to be a clear game-breaking bug.

If, however, an enemy soldier tries to throw a grenade, just as another AI-controller soldier walks into the frame, and the grenade bounces off their head, blowing up the two characters, this is also bug-like, but the player will see this as humorous and memorable. It is, he said, the kind of story that they are more likely to share than one that has been meticulously scripted by a narrative designer.

“Emergent storytelling is one of the few ways in which video games can still truly surprise us,” said Popovich.