Masons are a group of players who can speak to each other privately and know that everyone in their group is not a member of the Mafia. Whether the Masons' ability to privately communicate can be used at any time or at Night only is up to the moderator's discretion. The number of Masons can vary from game to game, and it is not impossible for there to exist separate Mason groups within the same game.
If there is one Mason, there is always another. A single Mason is equivalent to an Innocent Child.
Masons are the central feature in the Open Setup Friends and Enemies.
The Mason role has generated a fair amount of controversy and a few offshoots. Be sure you ask the moderator what precisely it means to be a Mason, as all of the below have been known to simply be called "Mason".
Most notoriously, some moderators will introduce Mafia-aligned Masons, taking the term "Mason" to imply that it is probable that the other Masons are Town-aligned, and not absolute. These nonconfirmed Masons are supposed to be middling in certainty between Neighbors (see below) and confirmed Masons; however, this is impossible to mathematically verify. Alternatively, moderators may introduce Werewolves into Masonries (and likewise Mafia members into Monasteries) without bastardry, as the definition of a Mason or Monk is that they are confirmed not to be a member of a specific non-Town faction.
The term for players who know each other to be Town but are unable to speak to each other privately is Best Friends, though this has fallen into disuse.
To contrast, the standard term for players who do not know each others' alignments but can speak to each other privately is Neighbors.
There is nothing sacred about the Masons being forced to talk at Night only; allowing Masons to speak at all times raises their effectiveness somewhat.
Masons, regardless of when they are allowed to speak to each other, are considered Normal on mafiascum.net, provided they are Town-aligned. A Masonry must contain at least two Masons.
Use and Power
The most obvious power of a Masonry (and Best Friends) is the mutual confirmation of multiple players as Town. Consider that a Cop can find out over the span of two Nights that two other players are innocent, and if the Cop roleclaims effectively, the Town wins three confirmed-innocent players on Day 3. A three-person Masonry, on the other hand, has that same number of confirmed innocents from the start of the game. In addition, while a Cop's innocent results are mostly only useful if the Cop lives to claim them and is believed, each of the Masons can mutually confirm the others as soon as the existence of a Mason is made evident. (For instance, if someone dies overNight and flips Mason, the other Mason(s) can still claim and be considered confirmed Town.) Last, Mason is difficult (but not impossible) for scum to fakeclaim, as they need to put up a scumpartner to be their fake Mason partner and hope that neither of them die over the course of the game.
Some moderators consider two Masons to be a roughly equivalent substitute for a Cop.
The conversational aspect of Masons is not nearly as good (as opposed to with Neighbors, where the conversation is a means to the end of discerning the Neighbors' alignments). It can be used to allow the confirmed Town players to confer with each other and play strategically during the Day - much like scum do, but with the intent of helping the Town and confounding the scum instead of vice versa. To that end, the ability for Masons to speak to each other amplifies the skill of the Masons themselves, but has no inherent power by itself.