WARNING: The following article contains spoilers for Detective Pikachu, in theaters now.

Detective Pikachu, has only been in theaters for one weekend, yet speculation has begun about a potential sequel. The Pokémon games are known for their sprawling world, so it's a little surprising the franchise's first live-action film is based on a somewhat-obscure title. But it makes sense, as a movie can't very well adapt a journey that unfolds across an entire region, each gym battle feeling oddly the same as the last. It requires a more straightforward story.

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Of course, the movie leaves the door open for sequels. Mewtwo's story has yet to be told, for example. But among the more tantalizing hints is Formula R, which could be a way to introduce one of the darkest chapters in the Pokémon gaming world: Pokémon Colosseum.

Formula R

In Detective Pikachu, the villains utilize the enigmatic Formula R to turn Pokémon feral and violent. It's extracted from Mewtwo, packaged in vials, and then inhaled by either Pokémon or humans. While the movie has a specific use for Formula R (as a means to blend human and Pokémon into one being to "evolve humanity"), it primarily appears as a means to turn normally good, sweet pocket monsters into howling, screeching beasts.

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Formula R isn't an invention of the film; it appears in the game as well. As such, it's inherently different from the process used to turn Pokémon into Shadow Pokémon in Pokémon Colosseum. However, as with all things, the filmmakers can take creative liberty to continue the plot thread from one film to the next.

But we're getting ahead of ourselves. Before we can talk about Shadow Pokémon, we need to ask, what's Pokémon Colosseum?

Pokémon Colosseum

When the Gamecube arrived, it seemed inevitable that a Pokémon game would come to the console. The N64 brought players Pokémon Stadium 1 & 2Pokémon Snap, Pokémon Puzzle League and Hey You, Pikachu. These titles had their fans, sure, but none seemed anything like the handheld RPGs that won fans over in the first place.

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Pokémon Colosseum was the first 3D Pokémon RPG to hit a console. However, unlike the handheld main series games, this one had a tightly written plot. In the Orre Region, the evil Team Snagem is stealing Pokémon and using an enigmatic process to turn them into Shadow Pokémon. They're super-powerful, but also malignant. The main hero, who looks like he shops exclusively at Hot Topic, rides his motorcycle across the desert region in an attempt to purify the Shadow Pokémon. Together with his psychic partner, Rui, they steal Pokémon back from Team Snagem to purify them through battle.

The series is a sprawling epic that features some far darker iconography than the usual Pokémon games. The villains are far more ruthless and sadistic, the Orre Region is harsh and inhospitable, and the main character is stealing Pokémon. Fans at the time went wild for what amounted to a small, easy-to-play spinoff.

Shadow Pokémon

Shadow Pokémon play a huge role in the original Pokémon Colosseum and its sequel, Gale of Darkness, but what are they?

The method to creating Shadow Pokémon is never disclosed in the games. However, the process is artificial and mechanical in nature. The scientists of Team Snagem, most notably head scientist Ein, describe it as "shutting the door to their hearts." This process turns the Pokémon into angry, violent creatures that are more than willing to attack Pokémon and trainers alike. While Pokémon are inherently feeling, loving creatures, these lack those emotions, turning them into ideal weapons. It also grants them Shadow Powers, which are effective against all Pokémon.

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Of all the Shadow Pokémon, the most noteworthy is Shadow Lugia, the only one to change appearance due to the process.

To purify a Shadow Pokémon, one needs to train and love the Pokémon, then, finally, take them to a shrine to purify their spirits entirely. This further conflict between the natural purity of Pokémon and the technological cruelty of mankind sounds awfully familiar. Almost like the villains in Detective Pikachu, right?

Can Formula R Be Used to Make Shadow Pokémon?

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Obviously, Formula R was created long after Pokémon Colosseum was released. That Team Snagem's machines and Formula R have oddly similar effects on Pokémon is a coincidence in the games. However, that doesn't have to be the case in film. The filmmakers have already shown their willingness to embrace fan theories and alter the plots of the games they're adapting to work better. After all, in the Detective Pikachu game, you never learn what happens to Tim's father or why Pikachu can talk to the player. Also, the villain's plan is totally different.

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So could Formula R be appropriated by Team Snagem for a Pokémon Colosseum game? And, if so, could that be the next mystery our heroes solve? Could this next journey take them to Orre?

Perhaps Snagem scientists appropriate Formula R and try to reverse engineer their own version. Perhaps they use it in the Orre Region, which leads our heroes from the first film into Orre as supporting characters. However, the main character is a rebel fighter hoping to defeat Snagem by stealing and purifying Shadow Pokémon, thus combining the plots of Pokémon Colosseum and Detective Pikachu.

Also, it's a chance to bring in another spectacular legendary Pokémon: Lugia.

But Will It Happen?

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In short, it's impossible to know until the Pokémon Company and Legendary Pictures announce their plans for future films. However, it would be a terrific way to expand the lore of the Pokémon world while continuing to utilize threads from Detective Pikachu. It's entirely possible, as previous reports have indicated, the next Pokémon film will focus on Mewtwo and his origin in the Kanto Region.

However, by doing so, they miss the potential to adapt lesser-known games loved by fans that mainstream audiences haven't seen yet. Detective Pikachu worked in part because it's a contained story. Whatever Pokémon movie is next ought to learn from that. Or perhaps it'll just be an original sequel. Still, the idea of Formula R is too tempting not to utilize in new, creative ways.

Directed by Rob Letterman from a script written by Dan Hernandez and Benji Samit, Detective Pikachu stars Justice Smith, Kathryn Newton, Ken Watanabe and the voice of Ryan Reynolds.