In my opinion having a day and night kill immune bulletproof townie basically hands the game to the town. I can't think of a scenario where this would lead to a mafia win.
2 mafias do not balance this, because neither can kill him. 2 mafias really does nothing for balance, since they are against each other as well, and can kill each other, as we found out in night 1. It just adds some confusion when the town finds out about the second mafia.
