Will I run it? Maybe, some day. I haven't had much luck running games of late.
Anyway, I was thinking about the house rules I'd use if I did run it, and thought that the thought-process I went through might be interesting.
First, I go through a period of brainstorming, thinking about the qualities I'd like to see in the game that aren't part of D&D's default assumptions.
I come up with:
a dark and gritty noir-like feel:
- I don't want characters running around in heavy armor carrying giant weapons. Daggers, light (or hand) crossbows, clubs, and staffs should be the weapons of choice. Wearing a sword (while not illegal) will mark you as a troublemaker, and you'd be treated as such.
- Combat should be fast and quick, and should occur mainly in darkened rooms and alleys. It should often end with one side running away.
- Problems should be solvable with or without combat. The "with combat" option should often lead to more complications in the long run. This isn't the sort of game where killing your enemy outright solves everything.
- Good and evil are much more in shades of gray than in black and white.
- The city government, such as it is, isn't going to be overrun by the PCs - but many officials are susceptible to bribery.
- Naturalist-based characters probably won't be appropriate.
- Stuff that happens outside of the city is rarely as important as things that happen within it - external scenes are largely set pieces.
- The city should be cosmopolitan and exotic, but known to the PCs (at least on the surface).
- PCs need to be employable, both personality-wise and skill-wise.
- PCs shouldn't be bright-eyed and bushy-tailed, optimistic fools - but neither should they have seen it all already. I imagine the characters to be in the level 5-12 range.
- PCs should be imperfect heroes placed in even less-perfect situations.
Then lets look at each of these, in turn. I'll come up with one or more house rules (or setting changes/elements) for each.
- Much of this can be handled through social pressure, but I don't want to rob characters of their class abilities without giving them something in return. The unarmored Defense Bonus option is a good place to start. Also, giving someone a good reason to use a dagger over a sword would be nice. How about allowing a dagger to be drawn as a swift action, rather than a move action? Alternately, some sort of dagger-specific feat might be created.
- I want to speed up combat, but I don't want it to be too deadly to PCs. I'm not a fan of pointless character death. Encouraging rogue levels among PCs would be good - starting a combat with sneak attacks is a good way to shorten it. There are a number of methods of simplifying things at the table that I'd use (pre-rolled initiatives on index cards and that sort of thing). I don't know that a specific rule would help here. I do want to make it easier to run away, though. Perhaps allowing a Flee action - a DC 10 (+1 per opponent threatening you) Reflex save will allow you to avoid attacks of opportunity if, as a full-round action, you take a double move out of a threatened square and don't move into any other threatened square.
Problems solvable without combat:
- Wizards made sure that all character classes have something to do in a fight. I want to make sure that they all have something to do in a social situation. Aid Another actions help, but they aren't terribly exciting. Also, given the characters' jobs, they'll probably all need some social skills. I might simply say that characters can choose one skill from the list of (bluff, diplomacy, gather information, intimidate, and sense motive) and treat that as a class skill. I'm probably going to have to increase skill points anyway.
Shades of gray:
-This is more setting than rules. Factions exist, but they do so mainly in the shadows. The Society of Sensation is a social club. The Dustmen are cultists who have infiltrated the morticians guild. The Fraternity of Order is a secret society. Outer planes won't be defined in terms of Lawful/Chaotic/Good/Evil, but rather in terms of Logic/Passion/Peace/Conflict. Many elements of the former will map on to the latter.
-Again, mostly setting, though I may need to make up some guidelines for bribery. The problem here is less The Lady of Pain than the Dabus. I may make the latter more free-willed most of the time. Perhaps the Dabus are really spirits that possess city employees on occasion. I'll play with it.
-I'd allow the urban ranger variant from UA. I'd also consider an Urban Druid-like character who communes with city spirits or somesuch.
Centrality of the city:
-This is a setting/adventure design thing. I might do something to increase the likelihood that natives of Sigil will somehow end up back in Sigil.
Knowledge (local) is sort of a pain. It will need some attention. I'd want this reserved for things like knowing about secret societies and legends about things that aren't major landmarks. I don't want PCs to need this in order to locate a tavern, know the name of prominent residents, or know current events.
No psychopaths. No complete loners. Everyone should have some useful skills - more useful than a specialized Expert, at least. Flexibility is key. I think that starting characters at level 3 would be a minimum. I'm toying with the possibility of allowing characters to be gestalt up to level 3 for increased flexibility - but one side of the gestalt would have to be a class with no magical abilities (rogue, scout, fighter, or swashbuckler, mostly). If I did this and required that, by level 3, the character would have to have at least - say - 30 skill points, then I wouldn't have to worry about increasing skill point allotment.
I might play with the advancement rate. If I start them at level 3, I'd allow them to advance normally until level 5 or 6 so that they can advance/customize their character a bit as they begin playing. I'd then slow the advancement so as to stretch out the sweet spot (to level 12ish) that I'd identified. If things made it to that point, I'd figure out where to go from there.
I'd allow the character traits option, but not flaws. PCs should be distinctive, but not crippled.
Now, I need to go through the points I have above and condense them, stripping out the unnecessary stuff. I also have to address the issue of magic and how to reconcile it with the tone I am seeking.