The supernatural threat in Fear Itself is the Outer Dark, a dimension of horror and suffering inhabited by ghastly Creatures of Unremitting Horror. The Outer Dark is separated from our reality by a thin and fraying Membrane, through which monsters and psychic effluvia seep. This background is shared by Fear Itself and The Esoterrorists, but while player characters in The Esoterorrists are competent operatives, supported by a well-resourced international organisation, those in Fear Itself are ordinary people, and are not pitted against the Esoterrorists (or are otherwise oblivious to its presence), but instead directly fight against the Outer Dark. Not all Fear Itself GMs have to use the Outer Dark mythology, but it's ideally suited for stories of grisly terror and urban decay. In either case, tropes related to the Outer Dark apply equally to both games. The Book of Unremitting Horror, which details entities of the Outer Dark, serves as a supplement for both games.
This game provides examples of:
- Achilles' Heel: A Special Means of Dispatch is a method of killing or defeating an otherwise invincible monster. Just as werewolves can be wounded by silver, or vampires repelled with a cross, some Creatures of Unremitting Horror have special weaknesses that can be exploited.
- Anyone Can Die: Fear Itself is a horror game, in which your characters might well be horribly disfigured, slaughtered, or driven irrevocably insane.
- Aura Vision: To those with the sight to see, every living organism is surrounded by a nimbus of energy. By studying the colour and movement of this energy, they gain insight into people and animals: their general emotional state, their state of health, and any influence of a supernatural being.
- Closed Circle: Risk Factors are why you can't run away. The particular Risk Factors used depend on the game you're playing, and the GM will tell you what they are. All Risk Factors have two things in common: they draw you into the mystery, and ignoring Risk Factors hurts. When presented with a situation that triggers the Risk Factor, the character is obligated to plunge deeper into jeopardy, or suffer a loss of Stability say you decide not to go into the abandoned mine to look for your missing brother, even though you found a clue pointing there.
- Despair Event Horizon: Represented by the Despairing condition that Shattered characters could suffer from. There's no hope you've got to get out of here. For the rest of the adventure, your primary goal is escape, not solving the mystery. If this comes into conflict with your Risk Factors, then you must spend the Stability to ignore the Risk Factor and keep on running.
- Digital Piracy Is Evil: Fear Itself 1st Edition's character creation process asks the player to name the worst their character has ever done. The last example given is 'illegally downloaded a role playing game off the Internet, depriving starving writers of their rightfully deserved income'.
- Dreaming of Things to Come: Some psychics can receive visions of the future, which appear in the form of vivid waking dreams, with visual and auditory components. In some instances one may even detect smells or respond to climatic conditions like cold.
- Flash Back: The GM is advised to use flashbacks, in which characters enact scenes from their character's pasts, to surpirse both the spotlight player and others by throwing new light on their backstory, bringing alive a part of the character's background that usually stays in the player's head and in a description only the GM reads.
- I See Dead People: A medium can speak to the spirits of the dead. Or rather, they speak to discarnate entities, most of whom identify themselves as such. A typical medium believes that they're ghosts, communicating from the afterlife, but maybe they've begun to suspect that a more sinister explanation is at play.
- Jekyll & Hyde: Those suffering from the Blackout With Teeth condition will find themselves blacked out when losing it, as their worst self takes charge to keep them alive. When they wake up, they find they've done something abhorrent or callous in order to survive, such as sacrificing another player character to the monsters.
- Hopeless Boss Fight: There's a reason Fear Itself explicitly calls out Fleeing as an ability. Often, the dangers you'll face are overwhelming. In other roleplaying games, there's an assumption that the GM will play fair and never put you up against impossible odds; Fear Itself makes no such guarantees. Monsters may be invincible, or vulnerable only to a particular countermeasure that you've got to discover through investigation.
- Magic Is Evil: Psychic powers leave one's mind open to the malign probings of the Outer Dark. If a psychic character has so much as brushed against the machinations of Unremitting Horror, their psychic powers have, depending on the nature of their so-called gift, served as a conduit for unbearably nightmarish feelings, sendings or visions.
- Never Split the Party: One of the huge mistakes in horror movies is to split up in the face of danger: lone investigators get killed. Splitting up to cover more ground may refer to the area splattered by your innards when you're dismembered by a monster. A GM should always be encouraging players to do that.
- Police Are Useless: The horror genre tends toward a sceptical view of authority figures. If the authorities were any good, they'd be able to rescue you from the creeping things up in the abandoned house. Instead, they're never there when you need them, or are slaughtered as soon as they appear. GMs should enforce this convention stringently, cutting off player access to outside support, and warn players wanting to play the combat/investigation character that they're picking an especially fragile character type.
- Psychic Powers: From the beginning of time, certain individuals have been sensitive to otherworldly vibrations. These characters have special skills like aura reading, being a medium or having strange messengers or premonitions.
- Weird West: The Vendetta Run frame is set in the worst and weirdest West, a nightmarish distortion of reality and of history. The players all take the roles of Cowboys, members of the quasi-criminal ring of local rustlers and thieves in cahoots with Sheriff Behan, pursued by Wyatt Earp's supernatural Posse. The skies of Cochise County might glow red at night, the mountains shift and groan, the cacti sport howling faces.