You are playing Nightmare mode.

Forced: When a location in the staging are is explored, raise each player's threat by X, where X is that location's Mire value.

Often they floundered, stepping or falling hands–first into waters as noisome as a cesspool, till they were slimed and fouled almost up to their necks and stank in one another's nostrils. –The Two Towers

Begin with the standard quest deck and encounter deck for The Passage of the Marshes scenario.

Remove the following cards, in the specified quantities, from the standard encounter deck:

3x Groping Dead

3x Dead Things

3x Soft Mires

3x Haunted Mere

3x Bitter Reek

Then, shuffle the encounter cards in this Nightmare Deck into the remainder of the standard The Passage of the Marshes encounter deck.

Finally, flip this setup card over and place it next to the quest deck. Its effect remains active throughout the game, which is now ready to begin.