From publisher website:
Game Night Kits for The Lord of the Rings: The Card Game contain promotional material for up to four players and are designed to encourage play and build communities. Each kit includes new sets of cards, called Nightmare Decks, that enhance existing scenarios and challenge players in new ways. Prizes are also included to reward players for succeeding. As players set forth from the Shire, fight spiders, and confront Smaug, they will have to overcome all-new threats and evil tricks in the newest Nightmare Decks.
Nightmare Decks invite players to experience past adventures in an entirely new way, facing new challenges along the way. By removing certain cards from a pre-existing Encounter deck and replacing them with the cards in the Nightmare Deck, players can experience an entirely new version of the quest, taking their adventures into new realms of nightmare!