The Setup:
When I first started designing this game, I knew I wanted to include stuff from some of the many non-Mafia games we played at MeMeMeet. My original idea was far more complicated, involving cards that could be earned which would directly impact the Mafia game (for example, the sword thing from Halo, as a one-shot kill). In the end, I decided that would be either too random, too complicated, too boring, or all three. So instead, I went with the MeMeMeet Points system.
The games were loosely in one of four categories - Voting (STD, I'm the Boss), Psychology (Minority, Prisoner's Dilemma, Ultimatum, which are fairly well known in game theory), "Proper" (Things..., Texas Hold'em, games we actually played at MeMeMeet, but modified to fit your screen), and Whoring (52 Card Pickup, RPS). The Voting games were pre-determined to fall on days 3 and 5, with the Haunt starting on 4 as a Red Herring game. Otherwise, the order of the games was pretty much randomly determined before we started, except games of the same type wouldn't come back-to-back.
The point system was pretty arbitrary, with early games on a "who'd you beat" scale, and later games on a more direct scale. Obviously surviving longer was going to help, but I didn't want that to be the deciding factor, so players only got "free points" for playing the first few days. And with Prisoner's Dilemma, of course, there was the possibility of losing points.
Roles:
A few roles were obvious for inclusion, and once I had decided on the MeMeMeet Point system, "Point Whore" was one of them. I liked this role, though not much interested ended up happening with it. The intention was that they would have to try to help the town, since they were pro-town, but maybe not absolutely as much as they could, because they had the other condition as well. For example, doing poorly on the first game deliberately would have earned them their investigation, but there was a risk that they would die soon after, or just not be able to catch their target. Or, they could go hard after their target to try to take them out of the running for points, but might hurt the town in the process.
The Blank Green Card was the other "basic townie" role I included. No one tried sending choices, which surprised me, given that every time the card was used at MeMeMeet (outside of Halo Mafia), it had an ability of some sort.
The scum groups seemed pretty natrual to me. I wasn't sure to begin with whether to include *any* actual scummers, but MeMe and Dirge filled out the Concerned Parents nicely.
As for the Zombies, I think I mistakenly voted for Fletcher after he was already dead or something like that, and then accused him of being in the Zombie Mafia, so that's where they came from. In a later game, I was cult and could recruit anyone, even if they weren't actually playing (though they didn't have to agree to come in to the game). MeMe refused, but +1 joined even though he had already been killed, and that's where the recruit ability got its inspiration. Jimmy Hoffa seemed like a good third choice.
And then the obvious joke was to put Jimmy Hoffa as town, too.
The Lyncher role was used several times at MeMeMeet, and I like Serial Killers that actually have a chance of winning, so I created the Serial Lyncher. Given his three win conditions and his night time immunity, Pooky had an even better chance of winning this game than VM2 (and it really was random!).
The Suicidal was also used a couple times, and the "Jester" flavor worked, so I threw it in. Thesp was pretty close to pulling it off, and then Pooky figured him out, so I was happy with the role and its fairness overall.
As far as the town abilities, I kept with my general MO of weak investigators; Dracula was Miller-esque in his role name, and didn't directly find scum, while the Point Whores had their own agenda. We played a Hospital game or two, so I decided to throw in plenty of protections, blocking, and hiding; given the potential for three kills a night, I wanted to make it a little harder for those kills to actually go through (though in the end, Pooky didn't ever try to kill, and none of the other kills were stopped).
Overall, I was fairly pleased with the balance. Probably a few tweaks I'd make looking back on it now, but I always think that.
The spreadsheet is still not finished, unfortunately... maybe I won't put it off as long as the VM2 post-game, though.