Game of Mafia
A mob has formed...
The Game of Mafia is one in which the players are divided into teams (or factions) and must decide as a group who to exile (or lynch) from the group until only one team remains. Typically, the two teams are a relatively small Mafia group, and the much larger Town group. Given that the Town starts as the vast majority of the players, this would be a one-sided game were it not for how the Town players are not aware of who the other Townies are. As a result, the Mafia can try to blend in with the Town and sway the majority vote onto Townies, hoping to turn the Town against itself until the Mafia controls the majority vote and therefore the game.
At its heart, Mafia is a game pitting an uninformed majority against an informed minority. It (as well as variations on it) has been commercially rebranded numerous times, often with werewolf flavor, but the central idea of the game is the same.
<psychology experiment, Princeton, lots of stuff someone else can fill in>
A Model for the Game
Most games of Mafia require an outside moderator who knows (among other things) who is on which team. This moderator begins the game by secretly assigning roles to players. The moderator then calls upon the Mafia to secretly reveal who they are to each other. This is Pregame.
Then, the Day phase begins. The players as a group vote a player out via a majority vote. Players are not allowed to conclusively prove their role by showing everyone what role the moderator gave them, but beyond that, almost anything goes as players argue, accuse, plead, protest, beg, and flail in hopes of getting the vote to go toward someone they think is scum (or if they ARE scum, not themselves!). A player who is chosen by majority vote to be lynched is ceremoniously removed from the game as the moderator reveals to everyone what their role is. Players who are removed from the game may no longer take part.
At this time, all the players go inactive as the Night phase begins. Most players can do nothing but wait while the Mafia secretly chooses a player they wish to murder during the Night. There may also be Town players who have Night actions as indicated by their role. Separately, they may choose to take action toward someone, with varying results depending on their role.
The next Day begins with the moderator announcing that a player has been murdered by the Mafia, and the game continues anew.
The game is generally over when there is only one faction left in the game - either the Town has voted out all of the scum, or the Mafia has made it so that the Town is helpless but to get voted out of the game.
There are several variations on this process, but this is generally a model for how the game works.
F2F Mafia vs. Online Mafia
Mafia is usually played face-to-face. In this type of setting, it is much easier to catch scum by picking up on how well someone can lie convincingly. Players who draw scum tend to have a harder time acting like a member of the Town, simply because trying to convincingly lie is not something many people practice and is just harder for some people to do. Nonetheless, the scum players must find a way to deceive the others into APPEARING to be part of the good guys while pushing the vote onto someone else who actually IS a member of the Town. In some ways, the process is similar to poker - by watching the facial expressions and tics of the other players, you can determine who is bluffing.
Online, though, the expressions and idiosyncrasies of players become much harder to determine. You cannot, after all, watch as a player stutters to say something they know is not true - you just see the carefully vetted message at the end. This is why most people are simply not good at forum Mafia, and as a result Mafia tends to win quite a bit more. As a result, online games tend to feature more power roles in hopes of giving Town a better chance than they normally would have.