TL; DR (Mafia all-stars format)
15 Players per game
3 Mafia (2 Kill power until 2 Mafia remain)
1 Cop (Parity Cop, only checks alignment in comparison to previous player checked)
1 Medic (Can't save self, must alternate saves)
Never played mafia? Here's the long version.
The Town is a 15 member set up with a moderator. The basic rule set will follow the Mafia Allstars rules with 3 mafia members, 1 parity cop, 1 nerfed medic and 1 vigilante. The Town members (includes the cop, medic and vigilante) win when all the mafia are voted out. The mafia wins when they are an equal amount of mafia and town. The game is divided into 2 phases, day and night.
During the night phase, all players put their heads down. Then mafia members raise their heads and will point at a member of The Town to kill. When there are 3 mafia, they have 2 kill power, meaning that they can kill 2 people a night or use both kill power on one target. When there are 2 mafia or less, they only have 1 kill power. After mafia have finished their actions, they lower their heads.
Next, the parity cop will raise his or her head and will decide who they would like to check. He or she will point at the person they wish to "check." The moderator will tell the cop whether that person shares the same alignment (town vs mafia) as the previous person the cop checked during the previous night. During night 0, because there has been no previous night, the moderator will not be able to give the cop any information. When the cop is finished with his or her actions, they lower their head.
Then the nerfed medic will raise their head and point to an individual they would like to "save." If a target is saved, one kill power used against them during the night by either mafia or the vigilante is removed and that person will not die. The medic cannot save themselves and they cannot save the same person twice in a row. After the medic has finished his or her actions, they put their head down.
Finally the moderator will call for the vigilante to raise his or her head. The vigilante is a town aligned role that has 1 kill power to use during any night that he or she is alive but only once per game. Once that kill power has been used, the vigilante has no more actions during the night. It is up to the vigilante's own discretion when to use that kill power. Even if the vigilante is killed during the night, if he or she choses to use their kill power during that night, their target will still be affected by the vigilante's kill power. Once the vigilante has completed actions, The Town will all raise their heads and the Day cycle begins.
During the Day, The Town members will deliberate on who they believe is mafia. Members can levy a formal accusation against other members they believe to be mafia. For an official vote to go through, the formal must be "seconded" or supported by 1 additional member. At which point the formal'd target will give a defense and the accusers will decide if they wish to proceed with a vote. If they do, The Town will vote on whether to lynch/remove the accused from the game. For a vote to succeed, a majority of votes are required. The accused does not count in the total. If a vote fails, the accused cannot be formal'd again during that round. If no consensus can be reached, The Town can vote to pass the Day without a lynch. Once a vote passes to lynch or to pass, the Day ends and a new Night begins.