Eternal Darkness’ infamous sanity system patent has expired – so can anyone now copy it?

GameCube exclusive Eternal Darkness remains a cult classic among video game horror fans for its patented ‘sanity system’ – a series of paranoia-inducing effects meant to confuse the player and reflect your in-game character’s spiralling psyche.

While something of a gimmick, Eternal Darkness remains notorious today for the system – which included the game pulling stunts like pretending to crash or turn your TV off, or faking the deletion of your save file.

Whether a marketing tactic or not, Nintendo of America filed a very real patent for the sanity system back in 2000, which finally expired in 2021. And every so often since then – particularly with the recent discussion around Warner Bros holding the patent for Middle-earth: Shadow of Mordor’s Nemesis system until 2036 – the matter has resurfaced.

“It looks like the infamous patent on the sanity system from Eternal Darkness is now in the public domain,” wrote reddit user DocMemory, shortly after the patent’s time period ran out. “Let me just mention that I am not a lawyer and this should not constitute legal advice.”

But what if you did ask a lawyer, and did get legal advice? Could anyone now copy Eternal Darkness’ sanity system and use those same sanity effects for themselves? I was intrigued.

“You SHOULD be able to use whatever elements of an expired patent are necessary to its use (as described in the patent),” video game legal expert and creator of the Virtual Legality podcast Richard Hoeg told me.

“But NOT anything that is not ‘necessary’ (graphics, perhaps some specific implementations – eg, sanity effects – as that’s artistic expression rightly protected by copyright).”

In other words, while you might be able to implement a similar version of Eternal Darkness’ sanity system, directly copying elements from Eternal Darkness could prove more complicated.

Nintendo of America’s original patent describes a game system that incorporates a character’s sanity level “that is affected by occurrences in the game such as encountering a game creature or gruesome situation”. In short, the more bad stuff you see, the worse things get.

But there are nuances – your character can rest or progress through an area more slowly to mitigate the sanity system’s effects.

“As the character’s sanity level decreases, game play is effected such as by controlling game effects, audio effects, creating hallucinations and the like,” the patent continues. “In this context, the same game can be played differently each time it is played.”

The patent goes on to detail a list of possible hallucinations that players may experience as a result of the sanity system, including:

• Wall carvings coming to life and reaching out for the character
• Something in wall or under floor moving by the character (Frighteners type of thing)
• Statue watching the character (Head tracking)
• Suit of armour moving (Relaxed to on guard stance)
• Static statue or object that appears to follow the character when they’re not looking
• False doors that appear and disappear when the attempt to open is made
• Glowing eyes blinking in the darkness, yet when the area is illuminated they disappear
• Painting that shifts and changes along with its meaning
• Points of interest markers that the character’s head will watch

As well as a list of more physical effects that impact gameplay:

• Hallucination: lights go out, and a creature appears as lights come on, then the lights go back off, then the light comes back on and the creature is gone
• Stretching walls and corridors so they require more time to traverse
• Bleeding walls
• Enormous roar that emits from a tiny rodent (Mouse or rat)
• Dripping water from above, but when the character takes a second look it is now blood
• Shadows that appear to shift and change
• Character’s torch mysteriously blows out, loud noise then it is once again lit
• Faint maniacal laughter (That gets louder and louder as the character draws deeper into insanity)
• Ambient audio, such as a water drip could become louder as insanity increases, so a really insane character will occasionally have this irritating dripping sound to distract him
• Lagging shadow (the character’s shadow appears to follow the character)

Eternal Darkness sadly never got a sequel, though attempts at crowdfunding a spiritual successor were made by some of the game’s development team. Perhaps we should all just look forward to experiencing Eternal Darkness’ sanity effects as they were originally programmed, if and when the game gets a fresh release via the Switch 2’s Nintendo Switch Online GameCube catalogue.