It's not actually poop: A look at Slime Rancher's 'plort' system

Slime Rancher, a game about...ranching slimes...is one of those weird games that I only noticed once it hit Steam’s top sellers chart in January this year, seemingly coming out of nowhere.

The game instantly draws people in with its bouncy slimes, bright colors, and generally joyful attitude toward the player. And below the surface of visual cheeriness there is a potential depth to this Early Access game that designers can learn from.

But first, let’s talk a bit about how the main currency in this game is slime poop…

Ok to be fair, the “poop,” called “plort” in the game, is more of just a general byproduct of slimes that they produce after you feed them a piece of their preferred food. Nick Popovich, cofounder of Slime Rancher developer Monomi Park, explains plort:

“Yeah, it’s interesting. We knew that everyone would think that it’s like poop. That was never really the idea. But we were certainly fine to let people run with that,” he laughs. “I like to think that they’re such simple creatures that [pooping] almost really couldn’t happen. I always thought of [the plort production] as amoebas splitting – so like, [plorts are] non-sentient pieces of [slimes]. So, yeah, I guess you could call that manure or whatever.”

The plort system works, broadly, like this: Slimes are essentially hungry mouths, and as a slime rancher, you’re providing for them by giving them food. In return, you get their byproduct – “plort” – and you spend it in the game’s economy in order to further your means to be an excellent slime rancher. There are different ranch upgrades, unlockable areas, and containment tools that you can buy with plort.

Plort varies in value, and there is a variety of plort. More valuable plort is collected from rarer species of slimes. Rarer slimes come about when, well, when one species of slime eats the plort of another species of slime. But if you’re not careful, if a rarer species of slime eats plort of another species, it’ll turn into a tar slime, which are mean slimes that will eat your poor nice slimes, and can really cause your ranch to fall into turmoil if you’re not careful.

So without getting eyes-deep in the specifics of plort, you can see the opportunity for great depth in plort-based slime mutation and a plort-based economy.

This type of system isn’t unheard of – lots of games have you harvest and spend resources (maybe you’re working on one!), but not all of these kinds of games are as good or promising as Slime Rancher or other well-executed resource management games. Popovich says that Monomi Park (which started as two people and has grown to four following the game's success) focused on how to make actual resource collection fun. A lot of games might have a great underlying economic system, but that great system is sometimes never discovered or explored in-depth by players because that main point of interaction—the resource collection—is just not appealing.

Popovich says that your underlying economic system will become more interesting if your gameplay (e.g. wrangling slime, sucking plort and food into your “gun”) is interesting for players to engage with. “The backbone of Slime Rancher is a fun, one-minute loop, and I think that’s just good, smart design,” says Popovich. “Start small, and everything around it gets stronger.”

So with Slime Rancher, there are two sides to the same coin: On one side is the very organized spreadsheet of the mutation and economic system. On the other side is the actual wrangling of slimes, which are chaotic, unpredictable, needy, and therefore interesting to interact with and care for.

That’s one of the main lessons of Slime Rancher: To sharply design minute-to-minute action, which in turn makes players want to engage and explore the deeper underlying systems.

“Once you have your spreadsheet laid out, and you’re like, ‘yes, it will be an interesting economic environment,’ you better hope that the other stuff surrounding it, unless it’s just ‘Spreadsheets: The Game,’ is also similarly interesting and engaging,” says Popovich. “Otherwise, no one is going to know [about your great system].”

And people are engaging with Slime Rancher – Popovich announced last week that the game, still in Early Access, has sold over 200,000 units, all selling at the full $19.99 price tag. With the ConcernedApe-developed farming game Stardew Valley also recently topping the charts, there seems to be a niche to be filled when it comes to ranching and farming games, which is a welcome surprise to Popovich and his small team. Not long ago, he would've been more incredulous about Slime Rancher becoming a success.

“I don’t think you could’ve predicted that two games with Harvest Moon elements would be topping the charts this year,” he laughs. “If you would’ve told even me that in December of last year, I would’ve gone, ‘yeah…ok sure...’”