diff --git a/tools/simulate.mjs b/tools/simulate.mjs
index b98ed2a..df5b846 100644
--- a/tools/simulate.mjs
+++ b/tools/simulate.mjs
@@ -19,6 +19,7 @@
  * what lets a published table be verified instead of remembered.
  *
  *   node tools/simulate.mjs --creature keepers --party 4 --runs 400
+ *   node tools/simulate.mjs --creature tt_cordera_man --count 6 --spread
  *   node tools/simulate.mjs --creature keepers --party holloway,okonkwo,finch,rahimi
  *   node tools/simulate.mjs --creature tt_coat --count 4 --runs 400 --seed 11
  *   node tools/simulate.mjs --list
@@ -377,7 +378,9 @@ if (has("--list")) {
 const creatureKeys = (opt("--creature", "") || "").split(",").map(s => s.trim()).filter(Boolean);
 if (!creatureKeys.length) {
   console.error("usage: node tools/simulate.mjs --creature <key>[,<key>] [--count N] "
-    + "[--party N|name,name] [--runs N] [--seed N]\n       node tools/simulate.mjs --list");
+    + "[--party N|name,name] [--runs N] [--seed N]\n"
+    + "       node tools/simulate.mjs --creature <key> [--count N] --spread [--party-size N]\n"
+    + "       node tools/simulate.mjs --list");
   process.exit(1);
 }
 
@@ -409,6 +412,70 @@ if (/^\d+$/.test(partyArg)) {
   });
 }
 
+/* ------------------------------------------------------------------ spread */
+
+/**
+ * The same fight against EVERY party the duty roster can field.
+ *
+ * This exists because a single published number for an encounter turned out to be the
+ * wrong instrument. THROUGH TRAIN Act Three advertises one figure — "the party is wiped
+ * in 24% of runs" — and the honest answer for that fight is anywhere between 4% and 96%
+ * depending on which four agents the players picked at the start of the session. The
+ * armed postings walk it; four trades are massacred. A GM reading the single number is
+ * reading somebody else's game.
+ *
+ * Exhaustive rather than sampled: C(16,4) is 1820 parties and the whole sweep takes
+ * about half a minute, so the worst case reported IS the worst case rather than an
+ * estimate of it. A GM planning a session wants to know the actual floor.
+ */
+if (has("--spread")) {
+  const size = Number(opt("--party-size", 4));
+  const runs = Number(opt("--runs", 100));
+  const seed = Number(opt("--seed", 11));
+
+  const combos = [];
+  (function choose(start, picked) {
+    if (picked.length === size) return combos.push([...picked]);
+    for (let i = start; i < ROSTER.length; i++) { picked.push(i); choose(i + 1, picked); picked.pop(); }
+  })(0, []);
+
+  process.stderr.write(`measuring ${combos.length} parties of ${size}, ${runs} runs each...\n`);
+  const rows = combos.map(idx => {
+    const party = idx.map(i => ROSTER[i]);
+    const r = measure(party, enemySpecs, { runs, seed });
+    return { idx, party, wipe: r.wipeRate, down: r.downMean, hurt: r.hurtMean };
+  }).sort((a, b) => a.wipe - b.wipe);
+
+  const name = p => p.map(x => x.key.replace(/^pc_/, "")).join(", ");
+  const pc = x => `${(x * 100).toFixed(1)}%`;
+  const mid = rows[Math.floor(rows.length / 2)];
+
+  /* Each agent's average effect on the wipe rate across every party they appear in,
+     against the average of the ones they do not. This is the line a GM actually uses:
+     it says who to send, in points of wipe rate, for THIS fight. */
+  const effect = ROSTER.map((agent, i) => {
+    const inParty = rows.filter(r => r.idx.includes(i));
+    const out = rows.filter(r => !r.idx.includes(i));
+    const avg = xs => xs.reduce((a, b) => a + b.wipe, 0) / (xs.length || 1);
+    return { key: agent.key.replace(/^pc_/, ""), delta: (avg(inParty) - avg(out)) * 100 };
+  }).sort((a, b) => a.delta - b.delta);
+
+  console.log(`
+  SPREAD — ${enemySpecs.length} x ${enemySpecs[0].name}
+  every party of ${size} the duty roster can field: ${rows.length} of them, ${runs} runs each, seed ${seed}
+
+  safest    ${pc(rows[0].wipe).padStart(6)} wiped   ${name(rows[0].party)}
+  median    ${pc(mid.wipe).padStart(6)} wiped
+  hardest   ${pc(rows.at(-1).wipe).padStart(6)} wiped   ${name(rows.at(-1).party)}
+
+  Spread of ${(rows.at(-1).wipe - rows[0].wipe) * 100 >= 20 ? "" : "only "}${((rows.at(-1).wipe - rows[0].wipe) * 100).toFixed(0)} points across party choice.
+${(rows.at(-1).wipe - rows[0].wipe) > 0.2 ? "  One published number for this fight would be the wrong instrument.\n" : ""}
+  each agent's effect on the wipe rate, over every party they are in:
+${effect.map(e => `    ${e.key.padEnd(14)} ${e.delta >= 0 ? "+" : ""}${e.delta.toFixed(1)} points`).join("\n")}
+`);
+  process.exit(0);
+}
+
 const result = measure(partySpecs, enemySpecs, {
   runs: Number(opt("--runs", 400)),
   seed: Number(opt("--seed", 1))