Perhaps not mafia per se, but following the format of the players having to figure out who among them is the antagonist. There will be both RP and Challenges, should players come into conflict.
Basically, one player will be trying to eliminate the rest using the power of a Stand. There are two variations I have considered:
(I'll keep this spoiler free so you can still enjoy the source material)
The concept of Stands was envisioned as a way to make psychic powers visually interesting. The Stand user projects an image made of mental/spiritual energy, usually of a humanoid shape, which acts as an extension of themselves. This is known as a "Stand," because it "stands beside you." Not only can these Stands interact with the physical world (so telekinesis would pretty much be your stand walking over and picking up an object for you), but most also manifest strange powers.
In general, stands follow these rules, subject to bending:
-A person may only have one Stand at a time. Their Stand might have multiple bodies (like a swarm), and there are specific circumstances that may cause someone to gain a different Stand than they had previously, but they can only have one at a time.
-Stands can only be seen by other Stand users, except for Stands bound to physical objects. (So to a non-user, it'd probably look like traditional psychic powers)
-Damage to a Stand is usually reflected on the user's body, and vice versa. Swarm-type stands or stands with a shape that does not clearly correspond to their user's body are an exception, though great enough damage on one (or sufficient members of the swarm destroyed) will still generally be visible on the other.
-Stands have a limited range from the object they are bound to (usually the user's body), and a Stand's range is inversely proportional to how powerful it is.
-Only Stands can directly damage other Stands. For instance, a Stand throwing a rock would not be able to hurt another Stand with it. Though someone could have their Stand throw that rock at the enemy Stand's user
Everyone has a stand:All the players are Stand users. At first they will be unaware of what each others' stands are, having to figure that out through the course of the gameplay. The antagonist may be granted a more powerful stand than the rest. The antagonist must be both identified and defeated in order to lose. Players are free to pick and create their own stands, pending GM approval of course, but these must not be announced to the other players out of character.
Only the antagonist has a stand:Players must face a killer stand user without stands of their own. Perhaps they can acquire them later, but unlikely. Two possible win conditions: either on the identification of the antagonist to the group, or if at least one player can escape alive after the antagonist is identified. Needs more thought.
In either case, much of the game will be hidden from general view. There will be a map to move around, investigation/action phases to mark the passage of time, and challenges should someone be attacked, allowing for at least a small chance of escape rather than an automatic kill.
Also, I've never really run a Mafia before, so some advice on formatting the game would be helpful. Does this count as actual mafia, and should I move it to the appropriate subforum when the time comes?