New Moon, the first expansion for The Werewolves of Miller's Hollow, requires the base game in order to play and it adds to the game:

36 event cards
5 new roles for the villagers: the idiot, the elder, the piper, the scapegoat, the savior
9 new variants/playing suggestions, e.g., playing in the dark with a candle in front of each player's face and blowing the candle out when the player dies, or instead of the werewolves eating civilians, they contaminate the civilians, leaving them without rights or powers
Rules allowing for many game variants