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).