Boardgamegeek https://boardgamegeek.com/boardgameexpansion/194839/lord-rings-card-game-nightmare-deck-celebrimbors-s
English - Nightmare Decks allow you to revisit your favorite scenarios recast within the darker and deadlier shadows of Nightmare Mode. Each Nightmare Deck introduces new encounter cards that you exchange with specified cards from the adventure's standard encounter deck. The result is a more challenging adventure that comes full of novel and thematic new twists.