This seems to be where people put ideas, so I'll write thess ones here. I registered for this forum a while back but never bothered to make a post. Figured now is as good of a time as any. I can't claim credit for any of these roles, they were in WC3's mafia (made by the same guy) and I think they'd be fun to add to SC2 mafia too.
Neutral Killing - Terrorist
This role goes to someone's house and explodes, killing everyone who visits the house. The role was a bit underpowered in WC3 mafia, so perhaps the best way of going about it is having the terrorists on a team.
-----Edit: I should clarify that terrorist dies when using his power, so it is a one-time use.
Mafia - Surgeon
Pretty much a doctor for the mafia. Since Godfather is immune, the surgeon would most likely heal the 3rd mafioso that's usually in these games. Another fun idea is two surgeons so they can heal each other. Doing just that (minus the Godfather) could create an interesting dynamic, and its one I've used in WC3 mafia customs in the past.
Neutral - Zombie
Zombies select one person at night. If they die, they are revived as a zombie. Perhaps a way to make this role better would be
to allow each zombie to select a person to potentially revive, rather than just picking one. Zombies win when all other non-zombies are dead.
Neutral - Medium
Aligned with the zombie, the medium can talk to dead people at night. This could conceivably be a neutral benign role or a neutral evil role similar to the witch, but tweaks may be needed to make Medium good in that case.
Town - Cursed
Aligned with the town at start, this role becomes a zombie if they die at night. If they are lynched, they just die. A way to make this role more interesting is to make it recruitable by Mason Leaders (and also cult, but I think that was in WC3 mafia anyway). That way Mason/Cult games would be possible without citizens that potentially cause people to ragequit.
Again, none of these ideas are original, I just think they'd be fun to see again. I did think of a role just now. It's probably bad, but worth throwing out there.
Neutral - Gas Station Attendant
Anyone who visits this role gets doused in gasoline. He is immune to getting doused with gasoline himself. He wins with the Arsonist. I think the Arsonist is an underpowered role, so this may be a good way to increase its power and make the role more interesting. Obviously this would be a niche role like the Coroner (who is only good with Janitors and Disguisers in play), but it could be fun.
Any comments, suggestions, criticisms etc. are welcome. If this thread is in the wrong place feel free to move it.