A few things I'd like to see implemented for Mafia is a poisoner, another person who distracts, and a spy. Poisoners basically poison someone, who dies the next night or a few nights after. You know what spies and people who distract do. Day killers are always fun too.
There's actually a cool theme on PO Mafia called Armies/Rotom. Everyone starts out as a Denizen or Rotom, and then the Denizens are transformed into a new role by the bosses of four different teams, and then the four teams fight to win. In Rotom, you transform yourself into a forme and each forme has a different power. Then the formes fight to the death, until one team remains.
I don't know, some of these ideas might seem stupid, but I love playing Armies on the Mafia Channel.