For purposes of a "mafia setup" I will define mafia as an informed minority of two or more players vs. an uninformed majority. (with possibility for multiple informed minorities)
Issue: While a game like this could be fun, it doesn't fit the definition of mafia. With all equal teams, there is no uninformed majority or informed minority, resulting in a game where a lynch is nearly impossible to achieve at some points.
Issue: Mafia is a game of finding mafia through lies and connections. Key word being connections. Being able to partner search is an integral part of the game and without any partners a large aspect of the game is removed (partner searching).
Issue: Coming from sites that focus on nightplay, many players love to include cults and jesters in their setups. The problem is tat cults and jesters are very difficult to balance around and can not just be thrown in to "add chaos". Cults are an issue because factional conversion as power is exceedingly powerful without balances within the setup. Jesters are an issue because it punishes town for recognizing someone acting scummy, which is the point of mafia.
Issue: Coming from sites that focus on nightplay, many players love to include as many named roles as possible to create a game that is "more fun." This does not work at mafiascum for multiple reasons. First off, and most obviously, having too many named roles allows for the breaking strategy of Mass Claim. Players simply claim their roles day 1, forcing the mafia to fake claim a role. This increases the chance of a town victory ten fold by creating multiple confirmed town players and eventually confirmed scum. Second off, the more power roles you include the swingier the game becomes. Third off, Mafiascum as a site focuses on day play, and it's typical for open setups to sometimes only contain 2-3 power roles.
Issue: This setup is broken via Follow the Cop. Follow the Cop strategy is where the Cop claims day 1, allowing the Doctor to protect him every night and confirming him as town if the mafia do not counter claim. He will survive for as long as the Doctor does, ensuring at least 1 night of public reports and likely more.
Issue: This setup is far to based on one role to make it interesting/fun. If the role dies night 1, the whole possible mechanic of the setup is over with and it becomes an uphill battle. Implementing a mechanic into the setup instead of specifically one player is generally a good away to avoid "Super Roles."
Issue: Silencer, whether removin vote or just ability to talk, typically just ends up with a player not having fun. Death miller is not as fun as you'd think. Percentage roles can make a team lose just because of luck. All of these roles can work in certain setups, but in general be wary of them.
Issue: The Doctors can claim day 1, protecting each other and causing them to both become unkillable, making the game nearly impossible. Even if a Mafia Roleblocker is included, if the roleblocker dies they become bulletproof, creating an enormous swing within the setup. This is generally fixable by making the Docs macho.