This worksheet reflects my opinions of how a game is best balanced. I am not the sole authority on Mafia balance. If anyone disagrees with assertions made here, I'd love to talk about it in the thread below. Even better, if you have things you'd like to see added or questions about balance, put them here!

Rules and Mechanics with One Mafia Team *a separate worksheet for multiple mafia teams may come later
Strongly pro-civilian
• Open setup heavy in unique roles (if reveals are legal)
• Unlimited BTSC for all players
Moderately pro-civilian
• Semi-open or matrix setup heavy in unique roles (if reveals are legal)
Slightly pro-civilian
• Semi-open or matrix setup light in unique roles (if reveals are legal)
• Closed setup heavy in unique roles (if reveals are legal)
• Potentially civilian-friendly independent roles
• Open thread during night phase
Barely pro-civilian
• Plurality voting
• Mafia BTSC made public after a game ends
• Open setup light in unique roles (like an open heist)
• Dead mafia in BTSC illegal
• No double-killing rule for the mafia team
Barely pro-mafia
• Majority/hammer voting (if vote changes are legal)
• Mafia BTSC during day phase legal
Slightly pro-mafia
• Closed setup light in unique roles (like a closed heist)
• Dead mafia in BTSC legal
• Precise roles of night killed players not revealed
• Locked thread during night phase
Moderately pro-mafia
• A rule against role reveals and info-dumping (not an issue in open setups heavy in unique roles, where the rule is necessary)
• A rule which limits vote changes to fewer than 2
• A rule which allows mafia members to submit actions on behalf of their teammates
• Alignments of night killed players not revealed
• Allowing mafia members to submit actions for their teammates
Strongly pro-mafia
• A rule preventing any dead players from winning the game
• A rule preventing any vote changes
• A mechanic preventing any roles from being revealed upon death (lynched or killed)
Role Strength by Faction
Civilian roles
Strongest
• Anything with the capability to cause a resurrection*
• Anything with the capability to cause a recruitment*
• Broad alignment-checking roles (cops)
• Any role with the capability to skip or significantly shorten a night phase
Strong
• Roles which are automatically immune to one night kill (bulletproof)
• Investigative roles which can view who targets a selected player (watcher)
• Civilian pairs or trios (if more than that, it's even stronger) who can participate in BTSC from the beginning of the game (masons)
• Roles which can kill during the night phase (vigilante)
• Roles which combine multiple basic abilities with good utility (jailkeeper)
• Uninhibited protective roles (doctor)
• Lie detection roles
Helpful
• Investigative roles which can view who a selected player targets (tracker)
• Inhibited protective roles (bodyguard)
• Disruptive roles (misdirection roles, blocker, bus driver)
• Any civilian role which can freely change which player is lynched
• Civilian roles with more than the standard voting power (doublevoter, extra vote distributor), this is stronger in an open setup
• Messenger roles which can communicate anonymously with other players or the public thread
• Roles which can see snippets of BTSC content
• Roles which are immune to one lynch (significantly stronger in open setups, weaker and arguably harmful in closed setups)
Harmful
• A role without direct voting control or voting power (tree stump)
• Investigated or revealed improperly (miller)
• Passively can cause mafia benefit (beloved princess)
• Traitor roles within the civilian faction designed to serve the mafia in secret
Mafia roles
Strongest
• Anything with the capability to cause a resurrection*
• Anything with the capability to cause a recruitment*
• Any role which can be revealed to be anything other than itself upon death (seemer, role forger), slightly weaker when role claiming is legal and in an open setup
• Any mafia role which can freely change which player is lynched
• Any mafia role which is immune to even one lynch (weaker than a lynch switch but still very strong)
• Infiltration roles that can corrupt a civilian BTSC group (weaker in an open setup)
• Any role with the capability to skip or significantly shorten a day phase
• Role deactivator (permanent)
Strong
• Any role which can prevent a player's role from being revealed upon death (janitor)
• Any mafia role designed to counter a congruent town role (ninja, strongman, godfather)
• Disruptive roles (misdirection, blocker, bus driver)
• Investigative role which can identify roles of other players (role cop)
• Role stealer
• Silencer
Helpful
• Mafia roles with more than the standard voting power (double voter, extra vote distributor), this is weaker in an open setup and significantly stronger in a closed setup
• Cursing roles
Harmful
• Mafia member who is excluded from BTSC and/or unknown to teammates
How many players on each side?
NOTE: The numbers pictured below are intended to serve as a basic guideline. These assume a game is already balanced in other areas such as mechanics and role strength. These numbers may need to be adjusted to account for whatever unique balance-impacting elements have been incorporated into a game's makeup.
EDIT: needs revisions
Other significant balance issues:
• *A resurrection mechanic or role is a gigantic benefit to whichever faction possesses it. If this is to be included in any capacity, a strong counter-balance should be incorporated. If the resurrection is not guaranteed to affect a specific faction, it can still throw the balance of a game a great deal – consider weighting the effect with a negative consequence.
• *A recruitment mechanic or role is a gigantic benefit to whichever faction possesses it. If this is to be included in any capacity, a strong counter-balance should be incorporated. If the recruitment is not guaranteed to affect a specific faction, it can still throw the balance of a game a great deal – consider weighting the effect with a negative consequence. If the recruitment favors a mafia team, this can wholly decide who wins the game – it is the biggest possible benefit a mafia team can enjoy. If the recruitment benefits a civilian or independent team, it is a little less potent but still very significant. The only faction for whom recruitment isn’t inherently a huge power is the cult faction – it’s their basic function.