When the team behind the upcoming Luigi’s Mansion 3 decided they wanted to add co-op play to the game, they realized they needed a new character. And they came up with something novel: a strange, gooey version of Luigi appropriately called Gooigi. Many of us got our first glimpse of the slimy double during Nintendo’s E3 presentation this week. But, despite being designed with the third game in mind, Gooigi actually made a brief appearance in last year’s re-release of the original Luigi’s Mansion on the 3DS. For producer Yoshihito Ikebata, it was meant to be a tease.

“I wanted to put Gooigi in the 3DS version with no explanation whatsoever,” he says. “My hope was people would see him and be like: ‘What is this?’”

The reaction to Gooigi’s presence at E3 has certainly been strong, ranging from disgust to outright confusion. So first, here are a few facts about the slimy double. According to Nintendo, Gooigi is not a ghost, but is instead made of energy extracted from ghosts. It became sentient when Professor E. Gadd, a bumbling scientist in the game, spilled coffee on the energy. (When asked if the Jell-O-like substance is edible, producer Kensuke Tanabe said that “it might taste like coffee.”)

One of the most unsettling elements of Gooigi is how it interacts with Luigi. In the game’s single-player mode, you have to swap between the two characters to solve puzzles. Because of its less-than-solid makeup, Gooigi can slide through tight spaces to reach areas Luigi can’t. When you make this swap, Luigi’s body goes lifeless and limp. There’s some confusion over what exactly is happening here: Tanabe believes that Luigi has simply passed out, while Ikebata says “the essence of Luigi is sending Gooigi directions.”

The bizarre nature of Gooigi fits right in with Luigi’s Mansion 3, which shifts the tone of the series more closely to comedy. While there’s a spooky atmosphere — the game takes place in a haunted hotel filled with all kinds of ghosts — the moment-to-moment experience is largely slapstick. Luigi will cower in fear at almost anything, and the world has a very tactile nature. You can bump into objects and see them shake, and Luigi’s spirit-sucking vacuum can be used to do everything from shoot watermelons across the room to grab ghosts and smash them against, well, anything.

According to Tanabe, this kind of physical comedy can be hard to pull off in a game. So the team’s solution was to be a little extra. “We might think it’s fun, but then we put it in and people might get confused,” he says of the design process. “So we kind of jam-packed the game with all kinds of reactions by Luigi, and we hope that at least some of them hit the mark.” And a lot these moments work primarily because of who you’re controlling. “Luigi really helps with that,” Tanabe says of the game’s blundering lead.

The previous game in the series, Dark Moon, was something of a surprise hit, selling 6 million copies on the 3DS. This, coupled with Luigi’s Mansion 3’s prime placement as a major holiday Switch release, means that the new game could be yet another breakout hit. Which raises another interesting question: what would that success mean for Gooigi?

“There might be a Gooigi-only spinoff perhaps, with all different colors,” says Tanabe. “Gooigi Power Rangers.”