There are things out there Man was not meant to know. You're out to find them, but doing so may cost you your sanity.
Players begin with a number of sanity points, usually about 50 or 100 (use change, dice, paper or whatever to keep up with them). Many cards have a sanity cost to play (their corner value) and recovering sanity is very difficult.
There is a special type of thing called a Secret. Secrets don't do anything by themselves, but many other cards require certain Secrets. You can only control one of each type of secret at once.
The type of a thing will include any categories it belongs to, followed by any secrets required to play it. For example, the Walking Corpse is listed as Thing - Undead Creature - Magic. This means it counts as both an Undead and a Creature, and requires the Secret of Magic to play. An action will list any secrets required to play it. For example, Summon Tentacle Horror is listed as Action - Summoning, so it requires the Secret of Summoning to play.
Winning and Losing
A player is eliminated when they run out of sanity.
The last sane player is the winner.
This is a small part of a deck some friends and I had played around with a while ago. I don't have the deck anymore, but I thought someone else might want to use the idea. Also, I don't remember many details about the deck (such as how much a secret costs). There were four secrets, but I don't remember what they were now.
Well, this was a small part of a previous deck, but it's become its own thing now.
Also, the way I'm building the deck at the moment could be used to make this a CCG game. I'd never be able to make enough cards for that by myself though. (Would anyone play a Cthulhu CCG?)
Thing - Location
Destroy all secrets you control when you play this card. You cannot lose sanity while you control this. You cannot play any card that costs sanity while this is in play. At the beginning of each of your turns, regain 1 sanity. You may destroy this card at any time.
Thing - Undead Creature - Magic
Action: Destroy this card. Target player loses 1 sanity.
Action - Summoning
Target player loses 3 sanity or destroy target thing.
Thing - Book - Magic, Summoning
While you control this card, reduce the sanity cost of any Undead cards you play by 1 (min. 0).
Play this card only if you have less than half of your original sanity.
Choose one: Put one card from the discard pile into your hand or shuffle the discard pile (including this card) into the draw pile and draw one card.
Thing - Location
While you control this card, increase your maximum hand size by 1.
The Light of Dawn
Discard your hand, draw 5 cards and regain 2 sanity. Any player can discard a Shadow card to counter The Light of Dawn.
Thing - Creature - Magic, Summoning
Place an action card from your hand under Familiar when it's played. If you do not control the Secret of Magic and the Secret of Summoning at the end of your turn, lose 2 sanity and destroy this card and the card under it.
Action: Duplicate the effect of whatever card is under Familiar.
Thing - Creature - Shadow
When this card is played, choose a creature already on the board. Treat Living Shadow as an exact copy of that creature. If the target creature is destroyed, destroy Living Shadow.
All players who don't control any locations lose 2 sanity.
Temple of Shub-Niggurath
Thing - Hidden Temple Location
At the beginning of your turn, place a counter on the Temple of Shub-Niggurath.
Action: Destroy the Temple of Shub-Niggurath. For each counter that was on it, target player loses 1 sanity. This can be spread across multiple players.
Choose a hidden thing. That thing's controller loses sanity equal to its cost.
Thing - Hidden Creature
When Colour Out of Space is played, destroy target location. At the beginning of your turn, destroy target creature. That creatures controller loses 1 sanity. If Colour Out of Space is the only creature in play, destroy it and all players lose 3 sanity.
Action - Mind
Target player must destroy any locations they control. They lose 1 sanity for each such location.
Thing - Psycological - Mind
This card may be played onto any player. At the beginning of your turn, lose 1 sanity.
Action: Discard your hand to destroy Panphobia.
Destroy a secret you control to regain 5 sanity.
Action - Mind
Choose a psychological thing. Either destroy it or give control of it to target player.
Destroy target secret. That secret's controller loses 1 sanity.
Search for Ancient Knowledge
Thing - Quest
At the beginning of your turn, lose 1 sanity.
Action: Destroy this card to put a secret in the discard pile into your hand. This action cannot be used on the turn Search for Ancient Knowledge was played.
Thing - Psychological
Any sanity loss due to a creature is reduced by 1. At the beginning of your turn, if you control no creatures, lose 1 sanity.
Destroy target thing with a sanity cost. That thing's controller gains sanity equal to its cost.
Spark of Life
Thing - Internal - Magic
You may only play this onto a non-Living, non-Location Thing. That Thing is now considered Living.
The Centre of Your Mind
Thing - Internal Location
This card can only be played if you have between 40 and 80 sanity points. If your sanity points falls outside of that range while this is in play, it has no effect.
Action: Take any secret from play into your hand. It is considered yours for the rest of the game or until it is returned back to its owner by a card's effect.
Thing - Person
Action: Search through the draw pile and take the first Secret card. Then shuffle the draw pile. After you do this, return Mr. X to the draw pile.