Secret history of Buffy/Angel mafia:
The first idea for this setup was to have a lot of scum. Real multiball. This works well with the flavor, as there are lots of evil guys that Buffy/Angel have to deal with. So I wanted two scum factions and a SK. 3-2-1 seemed like as cool distribution for the faction sizes. That would mean the game had to be sufficiently large to accomodate that. I went through both show's main characters - that was fourteen already. I decided to also include Faith, because she's cool and plays a significant role in both shows. There you have it, 15 players. That should be enough.
Alignment needs to be somewhat apart from flavor, or things don't work out. I could have made Buffy a town member, just because she's Buffy, but then I could have made her an IC as well. So I consulted random.org and got this distribution:
Wolfram&Hart: Winifred Burkle, Angel, Lorne
Vampires: Xander Harris, Tara Maclay
Serial Killer: Buffy Summers
So then began wondering if I could actually use these characters while the whole thing still made sense, or if they had to be mere fakeclaims. Angel could have been evil as Angelus, no problem, but then he really should have fought for the Vampires. So it ended up being a fakeclaim. Fred had a clear scum counterpart - Illyria. Lorne, well, I thought it'd be nice to have him in there as himself, and flavorwise it's not completely out of the question to have him working for W&H, so there you have it.
Vampires are easy usually, because any human can become one. Still, I wanted at least one of the show's "main" fangs, so Xander was replaced by Drusilla.
Buffy as SK couldn't work in any way of course. But as the show itself regularly substitutes Buffy with a robot, I just thought "why not do the same?" The guy controlling the robot would then obviously have to be Warren.
Next came faction design. With three competing scum teams, you have to take extra care that there aren't just a dozen of night kills and the game ends without anyone having the opportunity to actually do anything. The cool thing to do was take away a night kill from one of the factions, and that worked well for W&H. I also wanted the factions to have some factional abilities, because it always sucks to have some crucial power on one of your teammates and then he dies D1. More factional powers = less swingy.
Flavorwise, it was clear that W&H should somehow be able to interact with the other scum. It took a while to figure out how, but in the end giving them the ability to make killing proposals was nice. I also needed to save them from being accidentally night killed, since without a kill of their own, they had a hard time already. Making them full bulletproof seemed like too much. An option to be bulletproof if you don't do anything at night gives the players the kind of hard decisions that I like to have in games. With that it was only natural to give them the additional buff of winning when they have the majority, as that would usually win them the game anyway if they decide to go into lockdown each night, and prevented stalemate situations between the scum factions.
For the vampires, my early notes say they should be "super-powered". A 2 person scum team in a 15 player game is definitely going to have a hard time. Having the ability to redirect between your own faction (and see what targets you) just seemed like a cool thing to do, it had no flavor inspiration. In the end, I liked that, and it worked well with their individual manipulative powers.
The items actually came into the picture pretty late, while designing roles for Dawn and sorting out stuff with Illyria. Both those roles wanted item stuff. So I thought, hey I can make that a full-on subtheme of the game. I googled for important magical objects in the Buffyverse and took those I thought would add something to the game.
To the characters!
Willow Rosenberg
The first role I really thought about, and these thoughts changed the setup a little. Since at the time I already settled on flavor from Buffy's sixth season, I wanted an option to include "Dark Willow". Now there was already a lot of scum and, well, she didn't roll scum so making her full anti-town was not an option. The win condition she ended up having is of course heavily inspired by the show and how her transformation happens there. It was clear that it should be Tara and Xander she has to protect, but both of these rolled vampire, so that would make her an unknowing ally of the vamire faction, which wasn't what I was going for. So I changed Xander back to being town, and took Gunn (who I had a hard time creating a unique role for anyway) as scum. I debated letting Willow know who Tara and Xander were, but in the end decided it would be more fun this way.
Now that the win condition was finished, she needed powers. Flavor Cop and Doctor both were obvious abilities which would help her reach her win con. And because in the show she gets stronger the darker she gets, I wanted something similar to happen here. This is why she gets additional powers. Giving her the option to revive people was nice. She only gets that ability when Tara dies because reviving Xander is such an obvious use of power, while reviving dead scum is very dangerous.
Illyria
It was clear very early that Illyria was way too powerful to simply be one of W&H's minions. I wanted something special for her, and also thought that it would be cool to create some tension within the W&H. It wasn't easy to formulate a win condition that wouldn't make it best play for Illyria to just "out" her teammates and still gave her enough room to not be tied to W&H.
A Survivor that only wins with non-town seemed good enough, but I also wanted W&H to have a way to force her into cooperation - which would in turn weaken her abilities - and from that arose the game of cat-and-mouse that is the Mutari control.
Illyria was also the reason to introduce time travel since it fitted her flavor perfectly. The non-town neighborizing was a late addition, trying to help Illyria to with with other players. If I were to run the game again, this is probably the one thing I would change. 2 alignment-checking roles within W&H are just too much if Illyria decides to straight up root for them. A standard neighborizer would have been sufficient here.
Lindsey McDonald
Lindsey was a natural choice for a W&H baddie. I struggled to find something flavorful for him to do, so I just thought, "what would be cool mechanically?" With the focus on Day actions I already had, I thought some kind of Day-JOAT would be fun. He gets the Dayvig because I always wanted a scum dayvig and it makes up for having no factional kill. The rest is just other stuff you can do during the Day. Doublevote is quite strong, but I thought it was sufficiently weakened by the Day action window (you couldn't just hammer someone at L-1). Treestumping is cool as it offers both protection and roleblocking. All the item stuff is there so that he can prevent Illyria from taking the Mutari control.
Lorne
I debated whether to use Lorne or another W&H player with Lorne as fakeclaim. In the end, I needed a fakeclaim for Illyria within W&H, and well there just aren't that many recognizable guys in the firm. With Lindsey and Lilah gone, I felt any other W&H employee would be meh. So I thought a bit about what Lorne could do. And I dare say his power is one of the most flavorful I have come up with. The 1-shot lynchproof is also flavorful, and I thought W&H needed all the boosts they could get.
Drusilla
Let's face it, Dru is the coolest of all of the vampire baddies in the Buffyverse. With only a 2-player scum team, I needed the Vampires to be strong. They get a Strongman kill because of that. The redirection stuff also was here early, because it worked well with the factional ability. Originally it was 2-shot, but man was that too crazy. Later I needed some other powers, read through flavor for inspiration, and came up with the Seer powers. Bulletproof lets Dru catch a bullet from Tara.
Tara Maclay
What does vamp!Tara do? I decided, the same as real Tara: magic. So she should have a couple of cool things she can do. A JOAT is good in a faction this small. But just standard JOAT seemed too boring, I wanted some spin to it. After thinking about powers for a bit, I thought "make all powers such that nobody is targetted" would be cool. Demon sensor is directly flavor-inspired, the rest are just other things you can do without targetting. It took me a while to figure out a good wording for the Psychotrooper, as there are very different Cops around.
Warren Mears
A SK needed to be even stronger than the vampires. Making him full Ninja gives him some safety to actually use his powers. The abduction was the first power I thought of - it is a take on a similar power from Lost Mafia that never came into play. Role Cop supports that power. The other powers are typical scum powers, helping to both spread confusion and stay alive. Making the kill poison was a last minute decision. I was worried that the pace of the game would be too fast otherwise.
Cordelia Chase
I wanted to see an Oracle in action, and Cordelia needed a role, so that worked out. Flavorwise, Cordy would sit at the headquarters and look stuff up. Some time later in development it became clear that not every player should know what each item does, and then it was cool to have a player who would always know what they do. Giving this power to the Masons was too easy, so Cordy got it. She also gets another way of communication as that works well with the investigative stuff. Vision Girl came relatively late, when I realized town didn't have a protective role yet. It's flavor-based and gives a decision between investigation and protection.
Xander Harris
This is the crazy role. I had a lot of fun designing it. Xander just grabs into the box, pulls something out and hopes it does something for him. Some of the powers want to target town, some want to target scum, some don't want to be used at all. There's a lot of strategic depth in how to best use the role, which is cool - for example, you could shoot all but one of your powers N1 and then have a guaranteed investigation the night after. Or you only use one power per night, and then when you get a result from it, you know on whom it is.
Wesley Wyndam-Pryce
This is another case of mechanics over flavor. Wesley had the JOAT before the Masonry. As you might notice, it has an "unusual targetting" theme. You can target dead players, multiple players, and even Night phases! When I decided to turn him into a Mason, I debated weakening these powers, but I didn't. Having the 1-shot powers makes the question when to best claim the masonry a tad more difficult.
Rupert Giles
This one is a bit embarrassing. Obviously the role is called Watcher, and I intended it to do just what a Watcher usually does. Then I messed up the wording, and when I realized, it was already D1 and DeDe had used the Watching. So I decided to stick with the Tracking instead. Demonologist is a cool power in a game where you don't get full role flips, as it helps figure stuff out, and figuring stuff out is such a fun thing in RMM. He was the first one I turned into a Mason (originally, I considered making him a Masonizer even. How crazy is that?) Then Wesley was the obvious Mason partner.
Faith Lehane
It's a good thing that Buffy turned out to be evil, since finding stuff to do for two Slayers would have been pretty difficult. Faith, as the Slayer, had to be strong. So she's a sort of allrounder: Kill, protect, block. Full vigilante would have added too much death per night, and having the "remorse self-roleblock" thing made the choice to kill less automatic. The Commuter is mostly flavor; it's a nod to the fact that she's the only character (aside from the bad guys) that is not in the main cast of either show, ever.
Anyanka
It was fun to turn Anya back into a demon. It also allowed me to include her unique power, which wouldn't have made sense for her as a human. When I took on fleshing out her role, I had already introduced time-travel and items, both elements helped to phrase this the best way possible.
The idea of course stems from her first appearance on the show, fulfilling Cordy's wish that Buffy never came to Sunnydale. So translating that turned it into "travel in time to block someone's power". But I wanted people to also be able to wish for other things. I always liked the Motivator role, and it seemed a good fit.
Now this role can turn extremely strong as blocking a night kill can revive a dead player AND confirm someone as scum in one swift stroke. To balance that out a bit, her powers are tied to an item. When it is destroyed, any player she might have resurrected drops dead again.
Spike
Spike's power to detect demons was pretty obvious from the flavor. This is also the reason why I included the demon/human categorization, though it ended up doing a couple of other things too. He also gets to make the risky Desperado move. I think it's nice how he can only do it if he didn't try to hurt a human the night before.
Dawn Summers
My early notes say she should be a Thief/Hider. Of course at that time there were no items yet. When I decided to go for them, it was obvious what the Thief should do. She can also secretly give items to players. I didn't want items to just leave the game when players die, so she snatches them as well. Overall, lots of item interaction. I would have loved to see this in play, but well, somebody has to die early.