post ways roles that are bad can become good
Journalist: differentiate between reports.
Janitor: erase wills. wills are pretty much the bane of this role.
Enforcer: instead of just preventing conversion (next to useless), prevent mafia from being converted and switch other conversions to traitor.
Paralyzer: give him two votes when he uses his power. it's situationally unlikely enough that he'll ever have a use for his power, the extra vote would help.
Fabricator: add keys to fab items. fab is already a good role, but nothing beats a false sense of security.
Lyncher: win on lynch, not on death, unless lynch is overturned. this would fix lyncher being unwinnable on tree/gallis
Siren: if siren predicts her killer, don't kill her. seriously. alternatively: drunk all visitors, in addition to killing if guessing correctly (which is still hard enough)
note this is the perspective of a sandbox player and if you play comp you might not agree because some crappy setup uses one of these roles and depends on its shortcomings