Postcard Cthulhu is a cooperative Worker Placement game, where the players are Researchers attempting to postpone Cthulhu from rising from his watery grave.
The game is played on a postcard using coins. Each player takes a turn flipping some of the coins in their hand of coins to determine where they are able to play. They then place one coin on the map and this activates the special ability of that particular location. It might allow the players to draw more coins or move coins on the map along arrows, for example.
Each turn the current player flips 3 coins for Cthulhu which causes Cthulhu to steal coins from the players or fill up the Carcosa track, limiting the maximum hand size of all players.
The players win if they can get 3 heads on two particular locations on the board and Cthulhu wins if it steals enough coins from the players or fills up the Carcosa track. The type of coins used is not important.