For the MVP awards, wining 20 games as MVP could take months, even years, considering not all games you play, you win and not all games you win, you win as MVP. Maybe this award, like Michelle suggested, should be subjected to votes. For example, every x amount of time, a thread is opened in which everyone proposes a candidate for this award based on overall performance. After that, there's a poll for everyone to vote one of the candidates presented.
As for the participation medals, I think that is a good motivation for users to sign up for mafia games. That helps to keep the mafia community alive, fluid, active and fun, which in the end, is the main goal.
The hosts are a little tricky to be quite frank because it is very subjective. Though I do believe good metrics for hosts are:
- punctuality
- overall organization of the game (constantly updates the OP thread, properly constructs write ups and all that things one needs to manage in games).
- creativity (which is rather subjective)
- overall helpfulness and readiness in clarifying confusions with the roles and/or mechanics of their game.