With two sets of One Deck Dungeon (or with the base set and an expansion), you can play as a four hero party. With four heroes, two encounter decks are shuffled together, and most things in the game are doubled.
Closed doors have two face-down cards, and when the party chooses to Enter a Room, they split up into two groups of two to face the two encounters. Each is resolved separately, as a 2P encounter.
The party chooses which order to resolve the encounters. A number of other changes are necessary, as well.
Four Player Changes
A four player game requires two sets of One Deck Dungeon, and the following changes to rules:
Setup: Each of the four players chooses a hero. Flip hero and experience level cards to the 2P side, and the stairs card to the 4P side. Place two potions on the Turn Reference, or four if on the novice challenge tier. Shuffle both decks together to form one encounter deck.
Time Passes: Spend four time instead of two, each turn.
Explore: Each closed door is two face-down cards in a stack. If you would create a stack with only one card, discard it.
Enter a Room: Flip both cards in the stack face-up to become one open door. The party must choose to flee or have two encounters.
Encounters: The party must split up into two pairs to have the two encounters. They may be resolved in either order. Damage from consequences and effects from an encounter must be assigned to a hero in that encounter. Each encounter requires all dungeon boxes to be filled, and all dice are cleared before the second encounter.
General Supply: For each encounter (or boss round), the dice in the general supply are divided into two identical supplies, one for each pair of heroes. When some dice have been exiled, divide by color as evenly as possible. The general supply should have 12 potion tokens in a 4P game.
+Loot: After both encounters are complete, the party chooses how to assign the two cards as loot. One hero can claim both cards, if desired.
Level Up: XP required to level up is doubled. The entire party levels up together, and gains two potions instead of one when doing so.
+Stairs: The 4P stairs card is used. Every time six tokens are placed on the stairs, any two heroes each take one damage token (even if not the heroes currently in an encounter).
Boss: The boss has double health. During each boss round, the party splits up into two pairs. Each pair, in turn, has a normal 2P round against the boss. If the first pair kills the boss, the game ends before the second pair has to fight.
The party can split up differently in each round. A boss special ability that happens at the start of each boss round happens separately for each pair.
Minotaur: X = 2 times damage, instead of 4 times damage.
Dungeon Abilities: Effects that trigger each turn, each explore action, or when entering a floor have their impact doubled.
Invisibility Potion: An invisibility potion skips an encounter for one pair of heroes. The other encounter is unaffected.
Poison: Split into two groups of two to each Resist Poison, any time the party is required to do so.
Hordes of the Things: This optional card can be added to 4P games to make them more challenging. Good luck!
Forest of Shadows Expansion Rules
In addition to damage and time, Forest of Shadows challenge boxes contain poison ( ) icons. If not covered, a poison icon causes a green poison token to be placed on a hero.
Poison is not damage. It builds up slowly and can become very dangerous if not dealt with. Each time the party takes an explore turn (and at the start of every boss round), they must Resist Poison, by rolling any one die.
If its value is higher than the number of poison tokens in the party, they are successful, and one poison token is removed. Otherwise, they fail. One poison token is still removed from a hero, but two damage tokens are added to the same hero.
Half of the encounter cards in Forest of Shadows have a leaf icon () next
to the card title. For each leaf on an open door when the party resists poison, add 1 to the roll. These represent antidote herbs scattered around the forest.
If there are no poison tokens in the general supply, place a damage token instead, for each poison token that would be placed.
Any effect that heals a damage token can instead remove a poison token.
The Resist Poison roll is only affected by skills, abilities, or effects that directly mention it.
Several effects call for a die or token to be exiled. An exiled die or token is placed in the game box, unavailable for the remainder of the game.
Hybrid Dungeon / Mixing Sets
You can mix cards from One Deck Dungeon with Forest of Shadows to create a hybrid encounter deck. Use 22 cards from each, specifically all the cards with a () or () next to the card's title. Use the Hybrid Dungeon side of the Resist Poison card, which changes success to no longer remove a poison token.
You can freely mix heroes from different sets. When selecting a dungeon, it should match the cards in the encounter deck. With a hybrid deck, you can use any dungeon.
For a 4P hybrid deck, mix all 44 cards from each of the two different sets together. Note that there will be only 8 poison tokens available in a 4P hybrid game.
The Forest of Shadows Turn Reference has a Cure potion instead of Healing. It passively adds healing to every potion you use, and to every potion token you gain.
When using the Turn Reference with the Cure potion, the party begins the game with one Basic Potion type available. Choose any one of the four on the card, and tuck it under the Cure potion during setup.
If you use a potion but have no damage to remove, the healing effect is lost
You can choose to spend a potion token anytime to use the Cure potion to heal one damage, it just isn't as efficient.
The party does not get an extra second potion token at the start of the game for the Basic Potion card.
Some Peril encounters have an arrow next to each choice, one with 'Item' and one with 'Skill' inside, pointing at that edge of the card.
The only way to take the item as loot is to make the item choice, likewise the only way to take the skill is to make the skill choice. You can take the card as XP with either choice.
As part of the Kickstarter campaign for Forest of Shadows, we've created some companion mini-stories and events that you can use while playing the game. It will direct you on what order to explore dungeons, and add some special rules.