This mechanic came to me pretty much out of the blue and is based on the idea that as a party interacts with the world, they leave good and bad impressions on those they encounter. These then get passed around by word of mouth and there is a possibility that any future NPC they meet will have heard something about them. It assumes that the PCs will start out as relative nobodies and build up their reputation, though it could be adapted if the PCs are somewhat known to begin with.
Start the campaign with the numbers 1 to 20 as a list, but nothing written against them yet. Any time the party does something, good or bad, that would leave an impression on people (something with living witnesses who are likely to talk about it), add it to the list. Examples might be…
1. Generous – Returning from the dungeon, the party bought beers for everyone at the tavern that night.
2. Ruthless – When hired to track down some thieves, the party brought back no prisoners for trial.
3. Brave – The party marched willingly into the Underdark, to rescue some stolen children.
4. Mercenary – The party refused to save an orphanage from bandits without payment.
Once the list of 20 is full, start replacing items, beginning with the oldest.
Every time the party encounters a semi-important NPC, roll a d20 and consult your list. If the number is occupied, the NPC has heard that one fact about the party; if the number is still blank, the NPC hasn’t heard of them.
Things to note:
This system naturally models a growing reputation. When the PCs start out, people are unlikely to have heard to them; as the list fills up, it becomes more likely that NPCs will have heard something. Old news also starts to get dropped in favour of recent developments.
If you want a very slow reputation build, use a d100 instead. If you always want a chance that someone won’t know anything about the party, don’t fill the 19 or 20 slots and start replacing at 18.
You should make the players aware of this system, as it allows them to actively manage their own reputation. They may think twice about slaughtering bandits if they know that it’s likely to make the list, or they may decide that it’s worth it anyway, or they may only remember afterwards and deliberately balance out the reputational hit by donating to the local church or something..
Obviously, you shouldn’t let the players game the system… they can’t just keep buying drinks for people until all the negative items get replaced. Maybe rule that any item can only appear once on the list; if the players want a perfect reputation, they need 20 different “good” acts in a row, with no “bad” ones.
Also, note that the response to the specific items will be entirely dependent on the NPC. Taking the first example above (Generous), NPCs might consider this a sign that the PCs are decent people, a sign that they are frivolous and not to be trusted with serious work or a sign that the PCs are soft and can be easily screwed over.
This could require you to be somewhat flexible as a result; an encounter might go differently than you’d planned if, by a 5% chance, the one thing that the villain has heard about the party is the one time they did something quite despicable.
I’ve not tried this in play yet, but next time I run an appropriate campaign, I may give it a go. If anyone spots any glaring pitfalls, do let me know in the comments.