Builder's Manual
The Player's Handbook is also the GM guide; everything a GM needs to know is already there for the players. What's left is the information only a GM or world builder needs, and all of that is in this Builder's Manual.
NPCs vs. Playable Characters
Every character you add to the world lives on one of two sheets: a Character or a Hostile. The choice is not about species, and it is not about how much roleplay depth they get. It is about progression: does this character advance by earning EXP, or are they a static character the party might only see once?
PLAYABLE CHARACTERS TRACK EXP
The Character type is for people who persist over time: the player characters themselves, and any friendly NPC or enemy who will show up more than once. Recurring faces whose growth matters across sessions. The editable driver is EXP. You record what they have earned, and the sheet derives their Level from it at 100 EXP per level. You award experience, the sheet handles the level. Effort converts into advancement automatically, and a character's EXP total is a running record of their history.
HOSTILES ARE SET BY LEVEL
The Hostile type is for the other side of the table: monsters and enemies that will not return, anything meant to be killed. The editable driver is Level. You set it directly, and the sheet derives the EXP from it at Level x 25 (Level 1 is worth 25 EXP, Level 2 is 50, Level 3 is 75, and so on). Level is a tuning dial: a stronger character means a higher level, but it should match the fiction and what the players can currently handle.
Hostile EXP is the reward for a single hostile. Each additional copy of the same hostile in one fight pays less, with diminishing returns. So 7 of the same Level 2 Hostile would pay 50, 25, 13, 7, 4, 2, and 1 EXP, totaling 102 EXP.
WHY THE SPLIT EXISTS
The two shapes encode two different promises.
A Hostile's EXP is an indicator to the players about what an encounter is worth. It must be stable, even if it's not knowable in advance: the GM sets it before the fight, and the table can trust it. Making Level the editable field keeps that promise fixed while you tune the difficulty.
A character's EXP is a record of play. It accumulates organically across sessions.
WHEN TO CONVERT
The two sheets share the same vocabulary (stats, skills, Shape, inventory), so moving a character between them is a copy, not a rebuild. Convert when their role at the table changes.
Hostile to Character: the adversary survived the session, joined the party, or simply became a recurring character and started needing to earn XP. Give them an EXP total and let them advance.
Character to Hostile: a character stops being played and becomes something to be fought. Fix their Level and let the EXP derive.