At the start of each game, you will choose an Episode box and an Elder One box and combine their components. The Episode will provide the map layout, the ritual you are trying to disrupt (and how to disrupt it), as well as the abilities of the monsters in the game. The Elder One will provide the big boss you will fight, with its own challenges, along with its special minions. Do not combine elements from other boxes.
1 to 5 players will control investigators, cooperating to win or lose the game together. In each game, the goal remains the same: disrupt the ritual, then kill the Elder One.