Eternal Darkness: Sanity's Requiem is a 2002 action-adventure video game developed by Silicon Knights and published by Nintendo for the GameCube.

The game follows the story of several characters across a period of two millennia and four different locations on Earth, as they contend with an ancient evil who seeks to enslave humanity.

Development on Eternal Darkness began after Nintendo, impressed with Silicon Knights' Blood Omen: Legacy of Kain (1996), contacted the company to propose a collaboration on an original mature title.

While Eternal Darkness was widely acclaimed by critics and won numerous awards, the game was a commercial failure, selling less than 500,000 copies worldwide.

Attempts by Dyack to make a spiritual successor entitled Shadow of the Eternals with his new studio Precursor Games failed both of their Kickstarter campaigns, leading to the project being placed on indefinite hold.

Each of these characters are different in terms of the game's three main parameters – health, sanity, and magick – and have access to a small selection of weapons that they can use in combat, though what they can use is determined by the time period that they lived in.

This choice not only determines which of the game's other three antagonists are aligned to the plot, but it also has subtle effects on the gameplay in chapters and intermission periods.

Red tinted enemies for example, are generally tougher, having more health and dealing more damage, making that story path a kind of unofficial hard mode.

As the bar becomes low, subtle changes to the environment and random unusual events begin to occur, which reflect the character's slackening grip on reality.

[3] Minor effects include a variety of things, such as a skewed camera angle, heads of statues following the character, and unsettling noises.

Fourth wall breaking effects such as "To Be Continued" promotions for a "sequel", and simulated errors and anomalies of the TV or GameCube can happen either from low or depleted sanity, or by a scripted event.

They include the "Forbidden City" underground temple complex in Persia; a Khmer temple in Angkor Thom, Cambodia; Oublié Cathedral in Amiens, France; and the Roivas Family Estate in Rhode Island, which leads to an ancient underground city named Ehn'gha beneath the mansion.

Alex decides to investigate the mansion for clues, and stumbles upon a secret room containing a book bound with human skin called the Tome of Eternal Darkness.

Pious returns to Persia in the Middle Ages to construct a Pillar of Flesh at the Forbidden City, as part of his master's plans.

Centuries later in 1991 AD, a Canadian firefighter named Michael Edwards works with his team to extinguish several major oil fires in the Middle East, following the end of the Gulf War.

After an explosion killed his entire team and trapped him in the Forbidden City, he is approached by Roberto's spirit, who gives him the artifact and instructs him to take it to the Roivas Family Estate.

The artifact representing the stronger Ancient is moved, by Pious, to Oublié Cathedral, in Amiens, France, in order to prevent it from being used against him.

In 814 AD, a Frankish messenger named Anthony, who stumbles upon the plot, travels to the then small monastery in order to warn him of the danger to his life.

When the location is reconstructed into a Cathedral long afterwards, Pious summons a creature called the Black Guardian, to protect the artifact that could defeat his master.

After nearly being killed by Pious, who disguised himself in order to accompany him, Edwin finds Ellia's body and is entrusted by her spirit with Mantorok's essence, which he eventually delivers to Edward a few weeks later.

Alongside the struggle to claim the powerful artifacts of the Ancients, the Roivas Family Estate in Rhode Island, U.S. holds secrets of its own.

In 1760 AD, Dr. Maximillian Roivas, a colonial ancestor of Alex and her grandfather, inherits his father's mansion in Rhode Island and decides to investigate its secrets.

Recovering the artifacts from within the mansion, she soon ventures into Ehn'gha and uses them with the city's machinery, in order to summon a rival Ancient to fight Pious' master.

Edward's spirit then acts quickly to use Ehn'gha's mechanism to send back the summoned Ancient before it can cause any harm to the world.

Nintendo contacted Silicon Knights, as they had been contemplating adding more mature games to their line-up, and the two companies began collaborating to produce Eternal Darkness.

"[6] The development team borrowed inspiration from Edgar Allan Poe, Lovecraftian horror, and the Eternal Champion character concept by Michael Moorcock.

[5] It would have required a large capacity N64 Game Pak,[7] including full voice recordings for cinematic sequences, and a surround sound option.

According to lead designer Ted Traver, Nintendo wanted more games in its GameCube lineup, and the cost of manufacturing cartridges was much higher than optical discs.

[16] Eternal Darkness: Sanity's Requiem received critical acclaim upon its release, with aggregated review scores of over 9/10 at both GameRankings and Metacritic.

The battle associated with Alex's Spirit sees the player needing to defeat Zero Suit Samus from the Metroid series as the screen is mirrored at random intervals.