This is more of an Idea for a series of Mafia games, rather than any one game.
At the beginning, it’s a small number of players (as in, 3). 2 vanilla town and 1 Vanilla Mafia.
The current host along with the winning team then decide how the next game’s setup should be minorly improved. For example, if the town won, they could add a Vanilla town into the setup. Then, the game runs again. The new game can be played with the same players along with new players.
The legacy games will run forever, or until players no longer want to play it.
The formula for the game, generalized:
A setup is played
One team wins
That team proposes an amendment to the game in some way.
The host either accepts it, or rejects it.
4.1 If it was rejected, repeat steps 3 and 4 again