The Callisto Protocol treats genre fans to classic themes and elements from past works of science fiction survival horror while offering unique new systems, a compelling original story, and its immersive gameplay design. And not to mention an alarming number of terrifying situations.

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Throughout your harrowing escape from Black Iron Prison on Callisto, you'll encounter certain references to other notable sci-fi films and horror games that have undoubtedly been an inspiration. But there also lie more hidden easter eggs that are easier to miss, especially when the Biophages are busy tearing you limb from limb. Below are a few of the ones that you may have skipped over.

Warning: potential plot spoilers ahead

12 Dead Space Throwback

Perhaps a more obvious one if you've played Dead Space, the eerie hint on the wall written in blood about handling enemies resurfaces again in The Callisto Protocol. It comes during the fourth chapter when a new Biophage that sprouts tentacles and mutates into a heavier brute is introduced.

The instructive message in Dead Space read: "cut off their limbs" and appeared right as you acquire the plasma cutter. "Shoot the tentacles" applies to these new creature types and is very important to follow because they will be tougher to kill once they mutate.

11 Eyes Wide Shut

A big reveal in the game’s final moments is the pulling of the curtain on who exactly is behind the Callisto Protocol. You come to find out that it’s not the work of a rogue Warden at Black Iron Prison but an entire cult known as The Commonality. And they hold conferences wearing peculiar masks that conceal their identities.

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You can look at some enclosed in a glass case just before the final stage, and the ominous gold masks instantly remind you of some of those worn in the infamous secret society scenes in Stanley Kubrick's 1999 Eyes Wide Shut film starring Tom Cruise and Nicole Kidman.

10 Influences Of Other Zombie Games

The influences of previous games from the genre on The Callisto Protocol are unquestionable and serve as an homage. The mechanic of collecting items by smashing glass cabinets around the prison is similar to Resident Evil Village. The Blind Biophages are closely modeled after Clickers from The Last of Us.

Both are blind and only attack if you make noise, so the stealth sections and the Blind's design in Callisto wonderfully capture that aesthetic. Jacob hanging upside down near the infected also mimics the sequence where Joel hangs upside down defending Ellie in The Last of Us.

9 References To Alien Films

The Callisto Protocol is full of references to Ridley Scott's Alien Universe of films, with lots of inspiration going into the design of the creatures and environment. There are bodies glued to walls covered by slimy organic matter from Biophage secretions and egg-like pods carrying leeches that pounce at you.

In particular, one of those infectious leeches attaches to Dani's face like a facehugger. The UJC space suits resemble those from Prometheus, the blood worm Biophages lunge from sacs that look like facehugger eggs, and Elias is from Farallon's Hope, a name sounding similar to the Hadley's Hope colony from Aliens.

8 Predator Area Design

The development team is clearly highlighting the sci-fi works that inspire them. Therefore, Alien won't be the only classic sci-fi reference you can spot in The Callisto Protocol, as there's also a clever Predator easter egg thrown in at the Habitat Dome in Black Iron.

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The area hosts a massive jungle with a vast treeline, and you hear what sounds awfully like the guttural chittering clicks of the Predator species from the films as soon as you make your way down. The creepy four-legged Biophage Rushers also jump in and out of the trees.

7 PUBG References

The original plan for The Callisto Protocol was for it to become a part of the PUBG Universe, but that didn't end up being the case. However, as a nod to this potential story direction and the parent publisher remaining Krafton, the battle royale PUBG still made its way into the game.

The recognizable helmet from the character on the cover art of PUBG is lying on a workstation table. A critical one pertaining to the narrative is that Dr. Mahler explains the Biophage infection also occurred on a planet called Paramo, which is the name of a volcano map from PUBG.

6 Darth Maul's Home Planet

When an actor like Sam Witwer appears in the cast, a reference to Star Wars mythology is inevitable. Witwer is known in the Star Wars Universe for voicing Darth Vader's Starkiller apprentice in The Force Unleashed games and Darth Maul in the animated Star Wars series.

In The Callisto Protocol, he plays antagonist Leon Ferris, and his Data-Bio reveals that his hometown was Rimohtad on the moon Io. That, of course, is Dathomir spelled backward, which is Darth Maul's place of origin. Kind of like God of War Ragnarok had with the Raeb and Bear McCreary easter egg.

5 Braindance Session

The memory-sharing technology available in The Callisto Protocol can't help but feel like a nod to the Braindance technology, or BD, from Cyberpunk 2077. BDs allow you to record and playback people's memories, as Dani does with an Arcas colonist through their CORE implants.

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Although it's there for a brief cutscene and something more cinematic than a fully playable mechanic as it is in Cyberpunk 2077, the inspiration is there. Cyberpunk incorporates it into the quests and transports you inside the memory to thoroughly examine it.

4 Greek Symbolism

Greek mythology and culture play a subtle role in the storytelling of The Callisto Protocol. Alpha from the Greek alphabet ascribes the most successful subject of the Biophage experiment, Leon Ferris, while others hold a much deeper meaning. Jupiter's moon Callisto is named after a nymph who bore a son named Arcas to Zeus.

And that becomes the name of the doomed colony the UJC established on Callisto 75 years prior. The ship that the main protagonist, Jacob Lee, pilots is called the UJC Charon, and its cargo of Biophage larvae certainly make it worthy of being named after the ferryman of the underworld. The mention of Kallipolis can allude to Plato’s vision of a utopian society.

3 Schofield Landmark

Glen Schofield was the co-creator of Dead Space and is now the founder of Striking Distance and director of The Callisto Protocol. It's only just that a piece of him should live on in some aspect of the story. And that comes in the form of having a ravine on the surface of Callisto named after him.

The description for a keycode hint within Richard Cids’ Data-Bio reads that “the bridge over Schofield Ravine was constructed as part of the abandoned terraforming program." It's a pretty significant plotline, so it's cool that his name becomes a part of it.