Carcosa Rising

From BoardGameGeek:

Carcosa Rising is the first expansion for Four against the Great Old Ones. It is based mainly on Mythos-related materials from Chambers and Bierce, drawn directly from the original sources. The disturbances caused by the upcoming Great Ritual have started to tear apart the fabric of reality, and well-known places have already been replaced by a distorted version of themselves coming from other dimensions. Meanwhile, the King in Yellow and its agent, the Pallid Mask, are manipulating events from behind the curtain, and poisoning the very thoughts of unsuspecting people. And who is the mysterious plump man that appears to be following the group? Carcosa Rising includes a new Investigator class (the Dreamer), three alternative versions of locations from the basic game, an entire new location (Carcosa), three event tables for traveling, possible attacks from the Pallid Mask (who takes control of the body of Investigators gone Insane), and a final Encounter with the King in Yellow. This is a non-standalone expansion. Players can choose to add any combination of elements from Carcosa Rising to the base game, mixing and matching materials to ensure that no two games will be the same. -description from the publisher