Call of Cthulhu Keeper Decks are designed to provide in-game resources, handy reference, and information. Use these decks to supplement scenarios, for inspiration when designing new encounters, to pass secret and important notes to players, and as a handy way to impart information. These decks can add new layers to plots, enhance the story, as well as introduce friendly or villainous non-player characters.

The decks are:

The Curious Characters Deck: A range of friends and foes, with game characteristics and backstories, providing additional NPCs and replacement investigators (48 cards);

The Phobia Deck: Detailing the effects of phobias, manias or episodes of madness, each card describes and advises on the consequences of investigator insanity (48 cards);

The Unfortunate Events Deck: All manner of strange, ill-fated and disastrous situations that can affect, hinder, and trouble your investigators. Use in game to add additional drama and upsets for your investigators. (48 cards);

The Weapons and Artifacts Deck: Detailing hand-to-hand melee weapons, firearms, and Cthulhu Mythos artifacts. Each card describes the weapon's game statistics, as well as supporting historical information (48 cards).