Cthulhu Dark is yet another one-page RPG, this time for Lovecraftian horror stories. It does not work well for sandbox games; for best results, have a premade scenario and a plot with beginning, plenty of middle, and a handful of endings. Cthulhu Dark was created by Graham Walmsley.
Player characters are referred to as "Investigators," regardless of their chosen career. For each Investigator, choose a name, a professional occupation, and write a very brief description. Each investigator also has an Insanity score, which starts at "1."
In almost all cases, one player will be the one who describes the settings, supporting characters, and so on. This player knows the plot, and reveals it to the other players bit by bit as the Investigators discover the awful truth. This player is referred to as the "Keeper," though people familiar with RPGs might use the term "Master."
Attempting a task that could have interesting or "interesting" consequences for failure prompts the player to roll dice to see what the outcome will be. The player will use up to three dice:
- One die if the task is within human capabilities
- One die if the task is within the Investigator's occupational expertise
- One differently-coloured die if the Investigator is willing to risk their own sanity to succeed
Of the dice rolled, choose the one showing the highest value as the result. A '1' is barely a success, possibly with problematic consequences. A '6' is an overwhelming success, possibly with benefits that can be used later. If the result is unsatisfactory, the player may reroll all the dice but must include the Insanity die in the reroll.
If the roll is for an investigation, a '1' gives you the barest minimum required to advance the plot, and may include disastrous omissions or mistakes. A '5' would get you everything you needed and wanted to know, and a '6' might give you more information than you feel comfortable with, and could prompt an Insanity roll.
When more than one Investigator wishes to work together on a task, every Investigator rolls dice as if they were making the attempt, and the highest die of all rolled is used.
If two or more Investigators are at odds and must compete, each rolls the relevant dice. Highest wins, and use the higher Insanity score to break ties. If Insanity scores are also tied, roll again.
There are no combat rules. Cultists are mooks, a battle with them is a normal challenge. If you must fight the inhuman creatures let loose upon the Earth, the Investigator(s) will assuredly fail and perish. Investigators should roll dice to hide or to escape instead.
Things "within human capabilities" include: picking locks, finding R'lyeh, decyphering ancient carvings, spotting something concealed, researching a building's history, rationalizing something horrific. Things that are not within human capabilities include: casting spells, understanding inhuman purpose, being effective in dreams. An Investigator can still do things outside human capabilities, but unless that Investigator has an esoteric and very specific occupation, the only die that can be rolled for the attempt would be the Insanity die.
A high success does not permit players to skip parts of the plot. Rolling a '6' won't let you find plane tickets to R'lyeh in your grandfather's attic, but would give you names and dates instead of just an address for cultist meetings.
When you manage to roll under the Investigator's Insanity score (thus avoiding increasing Insanity), that means the Investigator manages to "keep their act together" in great stress, it certainly does not mean the Investigator is fine nor okay with what's going on. When you roll above the Investigator's Insanity score, the Investigator fails to keep it together, and "loses it" a little bit more.
Among players who trust each other, a player who is not the Keeper might suggest an interesting way to fail after a roll is made for a challenge. This player would roll a single die, and if it is higher than the result value that was rolled, the interesting failure occurs. (Can the Investigator player still risk Insanity to get a re-roll after this?)