Mafia is the most popular non-debate game on DDO. There is almost always at least one mafia game going on, with several more games in sign-ups or ready to launch. Depending on the moderator, games may be open to all users or restricted to users who have played a certain number of mafia games; for example, the DDO Mafia University is aimed at beginners, but is open to a few experienced users as well.
In Mafia, the players are usually divided into one of two main factions - the town, who comprise between 2/3s to 3/4s of players, and the mafia, who comprise between 1/3 to 1/4 of players. Many games also include third-parties, who are not aligned with any faction. In general, town and third-party players know only their own affiliation, while mafia members know who all the other members of the mafia are and can communicate with them via a group PM. In general, the town wins when they eliminate all non-town players, while the mafia wins when they comprise 50% or more of all players. Third-parties have unique win conditions, such as surviving to the end of the game.
In most mafia games, players are assigned roles that grant them a certain power. A full list of mafia roles can be found here, but some games also feature original roles that were created specifically for that game. In addition to any roles individual mafia players have, the mafia also gets a factional kill at night.
Mafia is divided into two phases: day and night. Day phases are public, and players can comment publicly in a day phase thread, and each player can vote to lynch any other player. The day phase ends when a majority of players vote to lynch a certain player, or time expires. Once the day phase is over, the night phase begins. Night phases are private and take place in PMs - the mafia chooses one player to kill, and any other users with night roles choose their targets as well. After the night phase ends another day phase is started, and this pattern continues until the game ends.
The user TUF put together a leaderboard showing which users had been part of the winning factions in the most games. The list only includes those games that have been played in 2012, therefore it misses a large majority of games on the site..
There is currently a mafia ELO efforted, headed up by TUF and Ore_Ele, to bring in an alternative leaderboard style. ELO has been highly successful and vastly popular with the debating leaderboard and hopes are that it will do well with mafia as well.