Preludes are a type of card first introduced in Mountains of Madness that slightly modify the play style of any game. Players are given the option of choosing a random Prelude, choosing a specific Prelude, or optionally not choosing to use one.
Prelude effects always modify the game before the first round is played. Some of them allow for the use of the side boards that would normally not be in play for the Ancient One, or using the Mystic Ruins Encounter when Syzygy is not the Ancient One. Others simply modify game effects. In general, it makes the beginning of the game a bit more difficult by creating extra hurdles at the start, but allows the player to gain other effects to make up for this.
Typically, only one Prelude is in effect at a time, but players who wish to use more than one side board or encounter deck may choose to run more than one. If playing the Campaign mode, players use the Prelude matching the Ancient One in play, and the Ancient One that would be in play in the next game.
