In addition to monster encounter reactions, I use it for offers to potential hirelings, making deals with merchants and traders, negotiations with NPCs about jobs, hireling loyalty and more.
The way I use the reaction roll is when the players are asking an NPC for something, trying to make a deal, avoid a fight, or if I’m not sure of the mood of an NPC. It is usually how I answer the question, “How does this NPC feel about this situation going into the encounter?”
Once I have that result as a baseline, I will adjust the outcome based on what the players do. If they behave aggressively and the reaction roll is a 4, there’s going to be a fight. The response from a reaction roll of 12 might be the NPC trying to deescalate the situation.
I apply situational modifiers to the reaction roll like how far away the encounter takes, what’s happening at the time, the context of the meeting and so forth.
One of the modifiers I use is reputation.
Your reputation precedes you.
We all walk around with a certain set of assumptions, beliefs and biases. Some of those beliefs are based on our own experiences, some are based on stories other people have told us.
If you have moved to a new community and you need a plumber to fix a problem, you might ask your neighbor for recommendations. The past experiences of people in your neighborhood make up the reputation of a particular service provider. We often make decisions or approach situations based on reputation.
If a particular neighborhood has a reputation for being dangerous after dark, we will try to avoid it. If a particular profession has a reputation for exploitation, we will scrutinize the details of any agreement we make. Reputation is important.
If there is a significant interaction between the party or character and an NPC or NPC faction, I will mark down a reaction roll modifier to be applied in future encounters. Usually it is one pip but can be as much as a +3/-3.
I have a sheet of various notes about the party and mark down reputation modifiers there. I will often mark them down on any notes I have for a particular faction or town.
This modifier can go up or down depending on the PC’s actions. A faction that has negative experience with the party may swing back to neutral or even go positive if the party does something I think will effect the score.
Any time the party or a particular PC has an event I think an NPC will remember and tell his friends, colleagues, leaders, or neighbors about, I mark down the modifier. There is some referee judgement required.
If the party does something that greatly benefits the NPC or faction without asking for something in return, that’s going to be a +3. If they do something that benefits the party but royally screws a faction, that’ll be a -3.
NPC’s the player characters have never met may have already heard of them and formed an opinion about them. That’s the power of the reputation score. You can tell players directly or indirectly that this is going on. In an interaction with an NPC, they might say something like, “I’ve heard of you guys. You’re the ones who cleaned the monsters out of the old copper mine and gave some treasure to the villagers” Or the party may get the hint when they have to raise their offers for hirelings and link boys when every attempt at hiring fails.
You can tell the players they’ve developed a bad reputation in town and have a -2 modifier to all interactions with merchants. I tend to avoid this. I prefer to communicate to the players what their local reputation is by the behavior of the NPCs they interact with.
Example in actual play:
In my Dragon’s Bend campaign, the party gets a bonus to reaction rolls when interacting with the priests who serve in the temple at Oktar’s village. The party hosted a wrestling tournament and provided the prize money as well as livestock for sacrifices to the goddess Deena. The tournament was held in front of the temple and was dedicated to the goddess.
Wrestling is a major part of the culture and the warriors of Oktar’s warband were very pleased by the event. The purse was quite generous. They provided food and ale to the spectators. The party enjoys a bonus to reaction rolls with Oktar, Oktar’s warriors and the people in Oktar’s town. If the party encounters a group of warriors from Oktar’s tribe while traveling on the steppe, they will receive a bonus to the reaction roll once the warriors learn who they are.
On the other hand the party has had several run-ins with the bird folk.* The bird folk live quite a distance to the north but fly to the steppe to hunt large game and rob steppe people when there is a good opportunity. They nearly murdered the entire party in the first session of the campaign. Atticus goes out of his way to attack them whenever possible as they blinded him with a javelin and he holds a grudge. The party is well known to the tribe of bird folk and there is -3 to any reaction roll when dealing with them.
*Birhaakaman from Swords & Wizardry Monstrosities by Matt Finch