Monsters in Ravenloft will be more frequent in their uses of special abilities and chaining attacks together; in addition, several of them will set up ambushes for players to snare the overconfident. Even worse, players will deal with a real change in enemy composition when the game changes to night time, with more lethal monsters stalking the darkened forest as the moon creeps out. So you might not experience true terror, but you will be a bit more scared than you were before.
Source: Official Site