Game description from the publisher:
In Cthulhu Gloom, you make your intrepid investigators face the most terrible terrors and madness before helping them pass on to their inevitable doom. Unpleasant Dreams brings the wonders and horrors of the Dreamlands to the table. Mix the 55 transparent cards in this set together with your copy of Cthulhu Gloom to add morbid new Modifiers, Events, Stories, Transformations, and Untimely Deaths, and a new family that calls the Dreamlands their home. Can you survive the creeping chaos of Nyarlathotep? Will your shantak be a loyal mount, or will you meet your end when you approach Azathoth? Dive into your own unpleasant dreams to find out!
In addition to allowing for game play with up to six players, Unpleasant Dreams includes two new Character cards called Unwelcome Guests. Deal one or both face up to the table's center at the the start of the game. Guests "follow" the card types noted on them; no matter where it currently is, a living Guest immediately moves to join the family of the character on which one of its "trigger" cards is played. All its Modifiers are moved with it, and it's considered a member of that family until it moves again. This may delay the game's end if a final play draws a Guest to the near-winner's family!