Mythos Corruption – Random Cosmic Horror Effect Tables

Art by Damir Damsa Omić

We return to our Mythos Corruption framework, which provides an alternative to the classic Call of Cthulhu Sanity mechanic allowing the Keeper and players to move away from Insanity and mental health associations used in the traditional ruleset. We have previously discussed Vulnerability to address Mundane Horror and optional rules to help tailor Corruption to your game. Here we offer alternative tables for Cosmic Horror (Bouts of Madness) and Unsettled Reality (Indefinite Reality) for completeness sake. While the effects of Mythos Corruption may appear outwardly as Insanity, they represent profound alterations of the Investigator’s reality. 

Rather than purely punitive events, some Psychic Detonations may have both negative and positive features, which may be exploited by both Keepers and players.

1 – Time Displacement: The Investigator gets unstuck in time viewing things that happened before or after the present. They may witness events leading up to their moment of Psychic Detonation or travel further back in time, potentially revealing a useful clue. Their physical body remains in the present and may be subjected to harm (Unable to engage in combat with a penalty die for Dodge rolls)

2 – Mutation: The Investigator hallucinates a bodily mutation of the Keeper’s choosing, which could include a tentacle limb, nascent gills, or bat wings. Although the mutation may not be fully physically realized, the Investigator can attempt enhanced physical feats, such as reaching through a narrow slit, extended breath-holding, or long jumps, with greater chances of success. The Keeper may choose to enact consequences with or without Failure of a roll. 

3 – Blood Lust: A red veil descends over the Investigator’s vision and they lash out with fury against the closest threat with a bonus die and incremental increase in Damage Bonus (Keeper Rulebook p. 33). If no further enemies remain before the Psychic Detonation concludes, the Investigator will attack the nearest target. 

4 – Subservience: Corruption triggers a complete surrender to the Mythos, and the Investigator falls Prone (Keeper Rulebook p.128) in obeisance to whatever prompted the Psychic Detonation. 

5 – Insatiable Desire: A deep craving erupts within the Investigator and they begin to seek out the object of their Insatiable Desire, which could include another Investigator or NPC. Keeper and player may collaborate to select an appropriate object or roll on the “Mania” table (Keeper Rulebook p.161) for guidance. A low-level craving may persist following the resolution of Psychic Detonation.

6 – Into the Void:  Prompted by Cosmic Horror, the Investigator’s mind catapults into darkened space where they witness strange constellations, distant cold stars shedding strange blue light, and dissolved galaxies. A Keeper may allow contact with alien entities or Mythos deities in the void. Otherwise, the Investigator returns to consciousness 1d10 rounds later.

7 – Incessant Piping: A maddening cacophony fills the air surrounding the Investigator, who struggles to identify the origin of this unsettling tuneless noise. The Investigator cannot hear anything or effectively communicate with their fellows. Increased susceptibility to surprise attacks.

8 – Ascendance: The Investigator feels a great surge of power coursing through them. They feel destined for Godhood as they experience complete replenishment of their Magic Points and receive a bonus die for their POW rolls. If they know a spell(s), they must cast one to demonstrate their superiority. If not, they must demonstrate their dominance through speech and/or violence.

9 – Non-Euclidean Geometry: New patterns emerge. Pathways open up before the Investigator, but distances can become difficult to perceive in the new reality. Roll 1d10 each round to determine Investigator’s Move value and play results accordingly. 

10 – Unstoppable Dread: The Corruption provokes a profound fear response. A real or imagined threat seizes the Investigator’s attention and they expend all of their energy in fighting or fleeing this profound terror. Keeper and player may collaborate to select a suitable fear or consult/roll on the “Phobia” table (Keeper Rulebook p.160) for guidance. A low-level fear may persist following the resolution of Psychic Detonation.

As discussed in our optional rules post, Cognitive Turmoil serves as a replacement for Indefinite Insanity and represents a reversible condition for your players to overcome. You may choose to roll on the table or select an appropriate condition for the Investigator. You may also use the Unsettled Reality results to help summarize bouts of Corruption that overtake several Investigators or the entire party. 

1 – Impossible Landscapes –  Reality has become completely distorted and broken. The Investigator can no longer distinguish real from unreal. All Listen and Spot Hidden rolls suffer a Penalty die until Unsettled Reality is treated.

2 – Debauched – If illicit substances, mundane or arcane, present themselves to the Investigator, they must be consumed. Unless otherwise specified by circumstances, the Investigator’s DEX value will be halved for the purposes of Combat Initiative. Any use of Dexterity-related skills will require a Penalty die.

3 – Blood Bath – The Investigator responds to all episodes of Vulnerability and Violence with the Blood Lust effect described above, lasting 1d10 rounds. 

4 – Lost in Space & Time – The Investigator constantly spins out into the void and frequently becomes unsettled in time. Any time the Investigator experiences any additional Mythos Resistance (Sanity) loss, they experience Into the Void for 1d4 rounds (cumulative with Psychic Detonation). 

5 – Dark Inspiration – Through Corruption, the Investigator sees the secrets of True Reality.  The Keeper and player should discuss a shift in the Investigator’s alignment, which is comfortable to the player and appropriate for the campaign. This may mean the Investigator sheds morals and values, makes suggestions in support of their adversaries, or outright opposes their fellow Investigators. To counterbalance these actions, the Keeper should reveal useful knowledge to the Investigator gained through their actions and dark thinking. Treating Unsettled Reality may restore the Investigator, but you may suggest lingering effects… 

6 – Run Fast, Run Far – At any threat of violence or helplessness, the Investigator must make an immediate Vulnerability check with a Penalty die. If they fail, they immediately flee to safety until they recover from the Vulnerable state. Once out of harm’s way, they can resume normal actions, but cannot return to the scene of violence.

7 – Crumbling The spreading Corruption has weakened the Investigator, and they begin suffering an accelerated debilitation as the dark forces consume their mortal form. All STR and other physical skill rolls will suffer a Penalty die. If the Corruption remains untreated, an Investigator may suffer Constitution and Hitpoint penalties.  

8 – Erased Memory – A portion of the Investigator’s mind has been lost. Keeper and Investigator can select an important element of their backstory, a component of the campaign, or one of their fellow Investigators. If Unsettled Reality remains untreated, memory loss will progress.

9 – Comforting Obsession – Just as the Corruption takes hold, the Investigator latches on to an idea, object, person or practice and pursues it relentlessly, often to the detriment of their Investigative activities. The obsession crowds the Investigator’s thoughts, making all Intelligence and Education-related rolls suffer a Penalty die. As before, the Keeper and player may select a suitable obsession, use a prior Desire, or consult/roll on the “Mania” table.

10 – Lasting Terror – What may have once been a brief episode of fear brought on by the Corruption has now seized hold of the Investigator and they remain constantly vigilant. This persistently elevated state results in a penalty die for all Vulnerability rolls until Unsettled Reality is treated. As before, the Keeper and player may select a suitable fear, use a prior Dread, or consult/roll on the “Phobia” table.  

Keepers should feel free to modify the results and effects for these tables. You may prefer to use the tables from the Keeper Rulebook. In particular, you may wish to substitute the Ideology/Beliefs or Institutionalized result (p.159) for Dark Inspiration if you think this effect may be disruptive to your game or players. 

Cosmic Horror – Random Effect Table (PDF)

1 thought on “Mythos Corruption – Random Cosmic Horror Effect Tables

  1. Owen says:

    Another good read! Once again; I like how these alternative rules sidestep problematic elements baked into CoC and in many ways feel like a better fit with the overall Mythos.

    Still taking baby steps with my second campaign as Keeper, but some day I’d love to give these a go.

    Reply

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