That is, they are just an organization you can negotiate with; they are almost more of an event, or series of events. A monster you can't just go toe to toe with.
- Rate guilds with dice representing the number of thieves. Example: 6d6. Roll this to get the number of thieves at present.
- Every month, reroll the number of thieves. This represents fluctuations in membership due to deaths and recruitment. Thus, killing half the guild doesn't necessarily mean fewer thieves next month.
- On the lowest possible roll (all ones,) the dice rating drops by 1. On the highest (all sixes,) the rating increases by 1.
- The number of dice is the maximum number of thieves in any typical "patrol" of thieves. This is important if, for example, the PCs have pissed off the guild; it's how many thieves may potentially show up in a given area of town.
- The number of dice also equals the number of additional higher-level types. Half of these will be "heroic" level (4th level.) The rest will be evenly split between 6th and 8th levels, rounding in favor of 6th level. So, a 6d6 guild will have 3 thieves of 4th level, 2 of 6th, and 1 of 8th.
- Half the number of dice equals the maximum number of master thieves. For our 6d6 guild, there will be 1 to 3 master thieves. Reroll this every season.
- You also need a Guildmaster, and the guild's attitude toward the guildmaster. Make a reaction roll, perhaps using the d4+d8 reaction roll idea for more detail. Is the guild Hostile to its own master? And if so, are they harboring their resentment secretly (Earth,) lamenting openly about the loss of glory (Water,) engaged in political debate (Air,) or openly fighting (Fire)?
- If the Guildmaster is ever slain, use the guild's attitude as a guide to how the guild reacts to the slayers. If there is more than 1 master thief, roll another reaction for the guild's opinion about the succession: Hostile results mean contested leadership.