The Cthulhack: Cosmic Horror for ICRPG



My genre rules for Lovecraftian mystery investigation and other cosmic horror scenarios using ICRPG Master Edition

Can Index Card RPG do Sin City?

Nice! Did you have any thoughts about Sanity loss from various sources? I suppose each monster would have this listed as an ability? I guess you could either have different effort dice vs. the PC’s Heart of Sanity, or a die for each heart the monster has? That would be pretty brutal, maybe too much so. Of course, dread Cthulhu all but guaranteeing instant insanity is pretty logical.

EDIT: at the very least different effort dice would work for non-mythos SAN loss- 1d4 for surprised by dead body, 1d6 seeing someone raised as a zombie, etc.


In my games, the first time an investigator ever encounters a “mythos monster” in the campaign, that’s almost always a multi-point Sanity loss; it’s as if you were firmly grounded in our knowable objective reality, and then one day you have an incontrovertible experience and are forced to admit to yourself that aliens/vampires/tentacle monsters are real. After that, seeing a new kind of monster is pretty much always a loss of at least one point, but seeing the same kind can be tanked most of the time without losing sanity—unless it does something completely and unexpectedly horrific or uncanny in front of you. Then all bets are off…

Regaining sanity (up to a maximum of 10) is generally a slow process, although it can become a good way for your players to frame their character downtime, seeking assistance and activities that improve their mental health standing. When players complete quest objectives and/or defeat mythos monsters, I almost always restore at least one Sanity point to their PCs as a reward, or more than one if they are doing something epic like avenging another character or substantially reducing the short-term peril of a large group of people.

I will note that compared to the sanity mechanics in some games (like Call of Cthulhu 7e, where your Sanity is on a 0-100 scale), the loss of a single point of Sanity when using this hack is always significant, because someone who is “perfectly sane” with :heart: only has 10 points to lose! Therefore, I recommend that GMs weigh the situation carefully whenever they consider delivering a multi-point loss of Sanity. Having a good ebb and flow to the levels of PC Sanity helps keep the mechanic both playable and meaningful. That said, there are lots of ways for each GM to choose to apply the basic Sanity mechanics I outlined in the hack, and, like the use of Hero Coin it supplants, there’s really no wrong way to do it.

(One example of a cool optional rule is to allow players to decide in the moment when they roll a nat 20 whether to A) tally it normally as a Mastery point toward a new Trained Skill, or B) recover a point of Sanity.)


I’ve just finished my campaign and to be honest, I’ll change the entire sanity thing next time.

Here’s my plan:

  • As before, PCs roll CHA to protect against insanity.
  • Once failed, I’ll for a sanity condition (instead of sanity damage)
  • For that I use two dice: a “trigger dice” and a “reaction dice”. Both are wooden blocks (rough d6 shapes) with hand-written tags on it.
  • Trigger Die: Smell, Offender, Possession, Victim, Noise, Relationship
  • Reaction Die: Escape, Emotion, Paranoia, Amnesia, Aggression, Obsession

The basic idea is to add tag combinations to PCs to describe their descending sanity.

Example: The investigator watches somebody being dragged into a dark corner. Death screams can be heard. He fails is SAN check and describes his initial reaction. Then the GM rolls e.g. “Victim” (as trigger) and “Obsession” (as reaction). Possible interpretation: Each time the investigator is physically harmed, he reacts with obsessively avoiding dark corners. Maybe that condition blocks a LOOT slot (as @kagozaiku suggested to me, similar to Mausritter’s conditions).

The main idea is, that the PCs will be less and less “effectively playable” (see insanity downwards spiral in Call of Cthulhu). As a GM, I don’t like the idea of PCs going insane at a point of time (when SAN reaches 0), imho that’s a process. Furthermore, PCs can be played way longer and it may yield fun RP situations. We’ve had a player whose investigator went nuts each time he had lost something from his pockets.

Also, rolling like 1d4 sanity damage 2-3 times in a session is a bit too fast for my taste in terms of bringing down a PC. Depends on personal preferences I guess.


Those are some fantastic ideas for your Sanity mechanics, inspired and refined by some significant table time. I think those are great, and I like how the readily expand the narrative dimension of the game. It also shows how versatile ICRPG is for hacking genre-specific solutions for cosmic horror. Very well done!