Welcome to Leviathan. A number of prominent occult figures have recently been invited to Leviathan House to oversee a divination of the fate of the accursed place. Unfortunately, the hereafter and the unusual don't appreciate being gawked at. Despite having recruited, as one might rationally expect, almost entirely fraudulent mediums, the spirits have guided one whose power is true and terrible to the gathering. With good fortune, the collected readings of you lot of fraudsters will be enough knowledge of the inner workings of the unseen to prevent the destruction of you all. You might even, with some luck, escape with the promised lucre.
The players start the game as one of a number of different professions of medium, each with their own abilities, participating in a series of rounds called "divinations". One player is the true medium, and this is decided (in secret) at the beginning of the game. Take a number of medium cards equal to the number of players, with only one true medium, and shuffle & deal. Look at yours in secret; the significance of being the true medium will be clear at the end of the game.
At the start of the divination, a divination card is drawn by the active player and its two aspects are read to the group. It is then dropped to land on a random side. Divinations have power levels which are, at the end of the round, applied as points to a specified set of players. Each divination has two possible (and roughly opposite) aspects, which can be strategically swapped throughout the round. Other unpredictable effects can be brought in by summoning spirits, which have their own deck. Players can perform any one of a set of actions during their turn during a divination:
- Add to the divination's power
- Subtract from the divination's power
- Reverse the turn-passing direction
- Flip the divination card
- Set a divination countdown
- Summon a spirit
Any player can perform any of the above... but they're only qualified to do two without consequences. Each profession lists the set of actions in their repertoire, but in the absence of being questioned they can get away with performing any. On the other hand, if they are challenged they have to verify their skills. They have to reveal their profession to the group, and if their profession is qualified to perform the stated action they succeed and the challenger fails. Otherwise, the challenger succeeds and the current player fails. Either way, the successful player gains two points, and the unsuccessful one loses two. If they don't fail a challenge, the results of their action are processed. If a spirit is summoned, its effects are processed. If the player chooses to set the divination counter, it is set to the number of players, such that (if not interfered with) the round will end the next time it's their turn. At the end of the following turns, the counter is decreased by one. Once the counter reaches zero, the effects of the divination card are processed.
This continues until someone gets enough points to end the game; 10. Once the game is complete, the true medium is revealed and, if the score difference between the top player and the bottom is less than five points, the true medium has succeeded in preventing the frauds from gaining any meaningful personal control. If the true medium succeeds, they are the winner of the game. Otherwise, the highest scorer wins. Canonically, everyone else is dead and damned. Kudos/condolences respectively.