Are there rules governing playing more than one expansion? Arkham Horror has a couple rules when there is more than one side board attached, but I haven't seen any documentation on modifications to Eldritch Horror rules.

For an example of what I'm wondering, here is an excerpt from the Innsmouth Horror expansion for Arkham Horror, page 6:

The rules are unchanged when using more than one expansion city, except that the number of players should be counted as being one less for each expansion board in play beyond the first. So, if six players are playing a game using both Dunwich and Innsmouth (for a total of two expansion cities), they are counted as having one less player, for a total of five players. This modified number of players is used for such things as the monster limit and the maximum number of gates that can be open at once, and it reduces the level of difficulty for the players since they have so much more ground to cover.

  • I believe there is a rule (don't have the quoted text on hand) where each extra sideboard added allows the max number of roaming monsters to increase by one before terror level increases.
    – Joey
    Apr 9 '16 at 21:28
  • I added a documentation reference to the main question.
    – Joey
    Apr 9 '16 at 22:55

Short answer: No. There are no special rules for playing with more expansion.

Additional info: However, there were some special rules for playing with specific expansions.

On January 12 2016, FFG had posted an update which featured new Reference cards with a following description:

Due to the introduction of new mechanics in its expansions, the balance of Eldritch Horror has shifted. To remedy this, revised Reference cards have been created for use when playing with any of the following expansions: Mountains of Madness, Strange Remnants, Under the Pyramids. Below are the revised Reference cards.

This update only lasted a week. On January 19 another update renamed this cards to "variant" not "revised" reference cards.

With the introduction of new mechanics in Eldritch Horror expansions, some player groups may wish for a more difficult or more relaxed experience with certain player counts. The variant Reference cards shown below can be used to increase or decrease the game’s difficulty.

I think that the revised reference cards are what you are asking about.
Arkham Horror was becoming harder with each expansion added and needed a special rules to fix that.
Eldritch Horror was becoming a bit easier with each expansion added (other than "Forsaken Lore") and these cards have returned the difficulty back where it was in the core game.
That's my experience, at least.
You may find these new reference cards at the end of the official FAQ.


Expansions consist of a variety of components which may or may not be used according to the current scenario.

We include all standard components from each expansion in every game. This means all of the following:

  • Non-sideboard locations
  • Mythos cards
  • Playable characters
  • Preludes
  • Expeditions
  • Assets
  • Unique Assets
  • Artifacts
  • Spells
  • Conditions
  • Great Old Ones
  • Monsters
  • Epic monsters
  • Focus/Clue/Health tokens etc.
  • Gates

Regarding clue tokens or gates that are for a side-board not in play, we leave them in the game and if one is drawn, simply draw another. I find that is easier than sorting them out but do as you wish in that regard. If you do wish to remove a specific expansion, the cards have a small indicator on the front side of which expansion they are from.

Sideboards come into play in one of two ways:

  1. When a GOO is chosen that requires the use of that board, or
  2. When a prelude is chosen that requires the use of that board.

Mysterious Ruins are the same as sideboards. The are present when playing against the Syzygy GOO, or when drawing/choosing the Cosmic Alignment prelude.

This means that generally you will only have one of the sideboard/ruins used during a given game, and then you will include cards specific to the locations on that board, or the mystic ruins deck (from now on, when I say sideboards, include the mystic ruins deck as it is bought in to play in the same manner)

It also means however that multiple sideboards may be used when playing against a GOO that requires one sideboard, and starting with a prelude that requires the other sideboard. For instance one could choose to combat The Elder Things from the Mountains of Madness expansion, while drawing the Museum Heist prelude from Under the Pyramids. There is no official statement regarding extra rules here as far as I am aware. I have not tried it but I suspect for small player counts you would find it difficult to cover all the ground. If you want to make it easier than you could use the variant reference cards mentioned here.

There is no official way to play with both sideboards and ruins, however you could do so by allowing two preludes concurrently, eg: GOO = Nephren-Ka, Prelude1 = Antarctica, Prelude2 = Cosmic Alignment.

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