These are my game design principles for Cthulhu-inspired TTRPGs (and specifically for scenario/operation design in Delta Green) that build on one central premise: the game is about coming to terms with the malignancy of forces beyond human control and comprehension. These principles are draft, and written at a conceptual level, so they can guide both mechanics and narrative design.
1. The Malignancy of the Cosmos
Principle: The universe is not indifferent—it is actively hostile. Alien powers, strange geometries, and unknowable truths are not neutral curiosities but corrosive forces.
Design Implication: Any encounter with the Mythos (texts, rituals, beings, places) should always carry a cost: corruption, madness, bodily harm, or the unmaking of relationships, institutions, or even whole communities.
2. Power Brings Ruin
Principle: Knowledge and tools that grant power are themselves poisoned.
Design Implication: Mechanics for forbidden tomes, arcane rites, and alien artifacts should be double-edged—players gain capability at the cost of sanity, humanity, or trust. The most “successful” investigators may be the most damned.
3. Human Agency is Fragile
Principle: Human beings can act, but never decisively shape outcomes in the face of cosmic forces.
Design Implication: Characters can achieve small victories (rescuing people, delaying catastrophe, exposing cults) but never defeat the Mythos itself. System mechanics might enforce that outcomes decay over time: a sealed gate will reopen, a cult will regrow, a truth will spread despite suppression.
4. Revelation is Destructive
Principle: To see clearly is to lose oneself.
Design Implication: Discovery is central, but each revelation should undermine the investigator’s stability. Mechanical tracks (sanity, stability, resolve, identity) should degrade as characters learn more, forcing players to balance curiosity against survival.
5. Horror Emerges from the Ordinary
Principle: The uncanny is most terrifying when it ruptures the everyday.
Design Implication: The game should juxtapose normality (family dinners, local politics, everyday work) with intrusion by the incomprehensible. This contrast magnifies dread and grounds horror in the human scale.
6. Doom is Communal, Not Just Personal
Principle: The horror corrodes societies as well as individuals.
Design Implication: Mechanics should model how cosmic malignancy spreads: cult recruitment, corruption of institutions, breakdown of social trust. Players’ actions should ripple outward, sometimes accelerating collapse.
7. The Unknown Cannot Be Mastered
Principle: Cosmic horror resists categorization.
Design Implication: Random tables, dreamlike logic, or shifting rules can keep mysteries unfixed. The more players try to pin down the nature of a threat, the more it mutates or evades final explanation.
8. Tragedy, Not Triumph
Principle: The story arc of cosmic horror is tragic: courage and reason are noble but futile.
Design Implication: Endgames should rarely offer clean victories. Instead, they leave scars, silences, or temporary reprieves. The most players can hope for is to pass the burden forward or contain a disaster for one more night.
The House of Nerdery and Curios 