My thoughts.
Basically, I don't particularly think that multiple mafias will work well, but adding others as third party roles would be interesting. Feel free to completely ignore any of these, but these were my ideas.
Dopps
Keep the dopps as the primary mafia, make each of the other roles a 3rd party role. Dopps take over townspeople so for the most part, the roles are shared between Dopps and Townies.
Cultist Leader
Each night, the Cultist Leader can try to recruit someone to their cause. If they target a Dopp, the Dopp will eat them. If the target an Alien (or other 3rd party), the ability will fail. If the target a Human, the Human will become a Cultist, losing all other abilities. To win, the Cultists must make up the remainder of the town. If the Cultist Leader is killed, the Cultists lose the ability to recruit but can still win by trying to control the lynch. (aka, don't let your Leader get killed)
Vampire
Each night, the Vampire must target a player. Each target has a chance of each of the following happening:
- Nothing happens to the target. They know they were targeted by a Vampire.
- The player is drained of their abilities for a night and the next day (role-block plus). They know they were targeted by a Vampire.
- The player is killed by blood loss.
- The player is turned into a Vampire (losing all other abilities).
A Vampire cannot convert a Dopp or 3rd party. If either is targeted, one of the first three options will happen. If a Vampire selects an invalid target (or cannot otherwise feed--psychic warden or the like) for three nights in a row, they die from lack of nourishment.
To win, the Vampire must kill all non-Vampire players.
Werewolf
If a player is a Werewolf, they will not initially know it (probably just get Townie as their role).
Each night, there is a random chance that the Werewolf will target a random player.
In the morning, they will wake up and remember what they've done.
After that, they can control the ability (maybe?)
Alternatively, make it an ability rather than a role.
Then, if the they target anyone with a night action, there is a chance that they'll tear them apart again.
If they don't have an active night ability, they random choose a player as above.
Once they know they are a Werewolf, they can use their original ability or the Werewolf ability.
Thoughts?