This is not a standalone product. It requires a copy of Arkham Horror: The Card Game Core Set and The Forgotten Age deluxe expansion to play.

Following the events of Heart of the Elders, you and your team of investigators have journeyed deep into a series of caverns where a new world lays hidden from the outside world. Strange creatures that cannot be of this world have seemingly lived beneath the shell of the Earth for centuries. They are horrifying to look upon, but are they dangerous? Now within their domain, it may be best to go along with whatever they want, but how much can you trust them, and what might your naivete cost you? 

This Mythos Pack features a new mechanic that makes playing this scenario an out-of-body experience, as well as new player cards to customize your investigators' decks.