Slender terrifies me. I played it for the first time in a busy office during the middle of the day, and it made me jump.

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“ Slender’s origins are wonderfully murky. Like so many classic works of horror – from The Castle of Otranto to Ghost Watch – it tries to blur the distinction between itself and reality.

“ You can’t plead or even attack. You can only run, terrified, through the darkness, until you’re out of breath and hopelessly disorientated.

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“ So many games are fantasies of empowerment, in which you can save the world or slay a dragon or be Batman. Slender makes you vulnerable.

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And I’m not easily scared.But there’s more to it than just a cheap shock. Over the last week, it’s somehow burrowed its way deep into my unconscious like few games have before. I must have played it a dozen times now, and it still unsettles me. It’s an experience that you rarely find in the mainstream, and it’s already become one of my favourite games of the year. Like Dear Esther and Journey, it worries that narrow definition of what a game can be. It’s more of an exercise in setting a mood and creating an atmosphere, not fulfilling a series of objectives or racking up a high score.Slender’s origins are wonderfully murky. Like so many classic works of horror – from The Castle of Otranto to Ghost Watch – it tries to blur the distinction between itself and reality. It’s the latest elaboration of the Slender Man myth, which isn’t an ancient legend originating from a small village in a Baltic State, but the product of an online competition to create the eeriest pictures imaginable. He emerged not from our darkest nightmares but Adobe Photoshop.I’ve always loved horror, from literature and comics to television and film. I didn’t have irresponsible parents – they did their very best to ward off the terrors the local video store had to offer, but if you have thirst for it, you find ways around such good intentions.Why do I love horror so much? Well, I like how it doesn’t feel obligated to depict the world around us; it allows the imagination to wander, recklessly, up foggy alleyways and down ancient staircases, where the most provocative metaphors writhe in the darkness. It can tell stories and extract responses that few other genres can. It can be intellectual and visceral at the same time. It can be sublime, hinting at what lies beyond the very limits of reason, and it can also make you want to puke on your shoes.The image that has stuck with me the longest is from John Carpenter’s Halloween. I remember stumbling across the film for the first time late one night on BBC2, when I was around twelve years old. The opening credits with that haunting theme playing over the image of a grinning Jack-O-Lantern transfixed me. Nothing has stayed with me quite like watching that movie for the first time. It’s not because of those final scenes in which the masked killer, Michael Myers, brutally whittles down the cast of carefree teenage girls. It comes much earlier in those scenes, shot in the midday Californian sun, when Michael stalks his sister. He watches her from across the road as she discusses the plight of Hamlet in English class. He watches her from down the street, partially hidden by a hedge.It’s chilling because Michael Myers is fueled by this inhuman patience. He can’t be bargained or reasoned with. He’s implacably evil. That’s why the Halloween theme is so perfect; written in 5/4, it has no natural end, no natural point of termination. Like Myers himself, it’s relentless.Slender shares a lot with Halloween. It has the same disturbing elegance. Every playthrough starts off in the same way. You switch on a torch in the middle of a forest in the dead of night, and you’re instructed to collect 8 pages of a scattered manuscript. There’s no mini-map or compass to guide your search, so you fumble across the terrain, getting lost, getting turned around. Occasionally you come across an ominous landmark – an abandoned pickup, four intersecting brickwalls, a building with white tiles lining its corridors.The Slender Man, like Myers, can’t be reasoned with. And the game’s controls are so limited you can’t plead or even attack. You can only run, terrified, through the darkness, until you’re out of breath and hopelessly disorientated.The game is so effective because of a simple psychological ploy. The Slender Man will never spontaneously appear in front of you. (At least he never has in one my playthroughs.) So, to avoid being caught, the imperative is simple: Don’t Look Now. But the temptation to look behind you, to check that he’s not gaining ground, is overwhelming. Like so many works of horror, Slender punishes curiosity.In place of a plasma gun, you have a flickering torch; it doesn’t even function as a weapon, like it does in Alan Wake. Once you see the Slender Man, static starts to accumulate on the screen, and the only way to disperse it is by switching off the light. Plunging yourself voluntarily into the darkness is the only way to guarantee your safety. It’s a simple but ingenious mechanic – it’s a loop of terror. To save yourself, you have to scare yourself; you have to plunge yourself voluntarily into darkness or come face-to-face with the Slender Man.This kind of experience – one that necessitates patience and relies on thickening suspense for its effect – is increasingly absent from mainstream horror games. Arguably, the PlayStation 2 was the console on which this genre enjoyed its heyday, a time when technological limitations and conventions of the time – myopic draw distances, fogging, rough visuals, fixed cameras – inadvertently added to the sense of horror.But big-budget horror titles can’t afford to take those risks anymore. To appeal to bigger audiences, they’ve started tempering their scares with more and more action. Publishers openly acknowledge this compromise. EA label executive Frank Gibeau recently spoke about how the Dead Space series has incorporated more action in the hope of turning it into a “more broadly appealing franchise”. Action means accessibility, which in turn means more sales.I’m sure Dead Space 3 Horror alone might not make the kind of money expected of a triple-A action, but I would argue that for an effective horror game those kinds of budgets aren’t required. Slender proves that. Furthermore, I would argue that Dead Space doesn’t have to incorporate action to be profitable. Halloween proved that, as have countless other low-budget horror movies through the years. Paranormal Activity has a budget of $15,000 and has so far grossed $193,355,800. Publishers could learn a lot from Hollywood, which has always known the horror genre to be a potentially lucrative one.Good horror is relatively cheap to make, and that austerity sometimes even works to its advantage. Smaller Indie titles, like Amnesia and Anna, are now catering for the horror audience increasingly abandoned by mainstream games. Seek them out, but I would encourage you to start with Slender. Just don’t play it by yourself in the dark.

Daniel is IGN's UK Games Writer. You can be part of the world's worst cult by following him on IGN and Twitter