diff --git a/packages/chess/src/modifiers/descriptors/promotion-override.test.ts b/packages/chess/src/modifiers/descriptors/promotion-override.test.ts
new file mode 100644
index 0000000..b2819a0
--- /dev/null
+++ b/packages/chess/src/modifiers/descriptors/promotion-override.test.ts
@@ -0,0 +1,245 @@
+import { describe, it, expect } from "vitest";
+import { Session, type EntityId } from "@paratype/rete";
+import { MODIFIER_REGISTRY } from "../registry.js";
+import "./promotion-override.js";
+import { PROMOTION_OVERRIDE_DESCRIPTOR } from "./promotion-override.js";
+import type { PieceType, PieceColor, Square } from "../../schema.js";
+import { getPromotionMoves, applyPromotion } from "../../rules/promotion.js";
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+function setupSession(): Session {
+  return new Session({ autoFire: false });
+}
+
+function insertPiece(
+  session: Session,
+  id: number,
+  type: PieceType,
+  color: PieceColor,
+  square: Square,
+): EntityId {
+  const eid = id as EntityId;
+  session.insert(eid, "PieceType", type);
+  session.insert(eid, "Color", color);
+  session.insert(eid, "Position", square);
+  return eid;
+}
+
+// ─── Registry ────────────────────────────────────────────────────────────────
+
+describe("promotion-override descriptor — registry", () => {
+  it("registers in MODIFIER_REGISTRY under key 'promotion-override'", () => {
+    expect(MODIFIER_REGISTRY.has("promotion-override")).toBe(true);
+    expect(MODIFIER_REGISTRY.get("promotion-override")).toBe(PROMOTION_OVERRIDE_DESCRIPTOR);
+  });
+
+  it("has the correct id, attrName, and uiForm", () => {
+    expect(PROMOTION_OVERRIDE_DESCRIPTOR.id).toBe("promotion-override");
+    expect(PROMOTION_OVERRIDE_DESCRIPTOR.attrName).toBe("PromotionOverride");
+    expect(PROMOTION_OVERRIDE_DESCRIPTOR.uiForm).toBe("promotion-target");
+    expect(PROMOTION_OVERRIDE_DESCRIPTOR.stackingRule).toBe("priority-wins");
+  });
+});
+
+// ─── describe() ──────────────────────────────────────────────────────────────
+
+describe("promotion-override descriptor — describe()", () => {
+  it("returns 'Cannot promote' for 'disabled'", () => {
+    expect(PROMOTION_OVERRIDE_DESCRIPTOR.describe("disabled")).toBe("Cannot promote");
+  });
+
+  it("returns 'Promotes to queen' for 'queen'", () => {
+    expect(PROMOTION_OVERRIDE_DESCRIPTOR.describe("queen")).toBe("Promotes to queen");
+  });
+
+  it("returns 'Promotes to rook' for 'rook'", () => {
+    expect(PROMOTION_OVERRIDE_DESCRIPTOR.describe("rook")).toBe("Promotes to rook");
+  });
+
+  it("returns 'Promotes to bishop' for 'bishop'", () => {
+    expect(PROMOTION_OVERRIDE_DESCRIPTOR.describe("bishop")).toBe("Promotes to bishop");
+  });
+
+  it("returns 'Promotes to knight' for 'knight'", () => {
+    expect(PROMOTION_OVERRIDE_DESCRIPTOR.describe("knight")).toBe("Promotes to knight");
+  });
+});
+
+// ─── apply() ─────────────────────────────────────────────────────────────────
+
+describe("promotion-override descriptor — apply()", () => {
+  it("seeds PromotionOverride='bishop' fact on piece entity", () => {
+    const session = new Session();
+    const eid = session.nextId();
+    session.insert(eid, "PieceType", "pawn");
+
+    PROMOTION_OVERRIDE_DESCRIPTOR.apply(session, eid, "bishop");
+
+    expect(session.contains(eid, "PromotionOverride")).toBe(true);
+    expect(session.get(eid, "PromotionOverride")).toBe("bishop");
+  });
+
+  it("seeds PromotionOverride='disabled' fact on piece entity", () => {
+    const session = new Session();
+    const eid = session.nextId();
+    session.insert(eid, "PieceType", "pawn");
+
+    PROMOTION_OVERRIDE_DESCRIPTOR.apply(session, eid, "disabled");
+
+    expect(session.get(eid, "PromotionOverride")).toBe("disabled");
+  });
+});
+
+// ─── valueSchema ─────────────────────────────────────────────────────────────
+
+describe("promotion-override descriptor — valueSchema", () => {
+  const schema = PROMOTION_OVERRIDE_DESCRIPTOR.valueSchema;
+
+  it("accepts all 4 promotion piece types", () => {
+    expect(() => schema.parse("queen")).not.toThrow();
+    expect(() => schema.parse("rook")).not.toThrow();
+    expect(() => schema.parse("bishop")).not.toThrow();
+    expect(() => schema.parse("knight")).not.toThrow();
+  });
+
+  it("accepts 'disabled'", () => {
+    expect(() => schema.parse("disabled")).not.toThrow();
+  });
+
+  it("rejects 'king' (not a valid promotion target)", () => {
+    expect(() => schema.parse("king")).toThrow();
+  });
+
+  it("rejects 'pawn' (cannot promote to pawn)", () => {
+    expect(() => schema.parse("pawn")).toThrow();
+  });
+
+  it("rejects arbitrary strings", () => {
+    expect(() => schema.parse("dragon")).toThrow();
+    expect(() => schema.parse("")).toThrow();
+  });
+});
+
+// ─── Integration: getPromotionMoves ──────────────────────────────────────────
+
+describe("promotion-override — integration with getPromotionMoves", () => {
+  it("PromotionOverride='bishop': returns only bishop promotion move", () => {
+    const session = setupSession();
+    const pawn = insertPiece(session, 1, "pawn", "white", 52); // e7 → e8
+    session.insert(pawn, "PromotionOverride", "bishop");
+
+    const moves = getPromotionMoves(session, pawn);
+
+    expect(moves).toHaveLength(1);
+    const move = moves[0]!;
+    expect(move.promoteTo).toBe("bishop");
+    expect(move.to).toBe(60); // e8
+    expect(move.isCapture).toBe(false);
+  });
+
+  it("PromotionOverride='disabled': returns empty array (pawn cannot promote)", () => {
+    const session = setupSession();
+    const pawn = insertPiece(session, 1, "pawn", "white", 52); // e7
+    session.insert(pawn, "PromotionOverride", "disabled");
+
+    const moves = getPromotionMoves(session, pawn);
+
+    expect(moves).toEqual([]);
+  });
+
+  it("PromotionOverride='queen': returns only queen promotion move", () => {
+    const session = setupSession();
+    const pawn = insertPiece(session, 1, "pawn", "white", 52); // e7
+    session.insert(pawn, "PromotionOverride", "queen");
+
+    const moves = getPromotionMoves(session, pawn);
+
+    expect(moves).toHaveLength(1);
+    expect(moves[0]!.promoteTo).toBe("queen");
+  });
+
+  it("PromotionOverride='disabled' also suppresses capture-promotions", () => {
+    const session = setupSession();
+    const pawn = insertPiece(session, 1, "pawn", "white", 51); // d7
+    insertPiece(session, 2, "rook", "black", 60); // e8 — capturable enemy
+    session.insert(pawn, "PromotionOverride", "disabled");
+
+    const moves = getPromotionMoves(session, pawn);
+
+    expect(moves).toEqual([]);
+  });
+
+  it("PromotionOverride='knight': capture-promotion returns only knight captures", () => {
+    const session = setupSession();
+    const pawn = insertPiece(session, 1, "pawn", "white", 51); // d7
+    insertPiece(session, 2, "rook", "black", 60); // e8 — capturable enemy
+    insertPiece(session, 3, "queen", "white", 59); // d8 — ally blocks push
+    session.insert(pawn, "PromotionOverride", "knight");
+
+    const moves = getPromotionMoves(session, pawn);
+
+    // Only capture to e8 remains (d8 push blocked); override limits to knight
+    expect(moves).toHaveLength(1);
+    const knightMove = moves[0]!;
+    expect(knightMove.promoteTo).toBe("knight");
+    expect(knightMove.isCapture).toBe(true);
+  });
+
+  it("no PromotionOverride: returns all 4 standard promotion variants (baseline)", () => {
+    const session = setupSession();
+    const pawn = insertPiece(session, 1, "pawn", "white", 52); // e7
+
+    const moves = getPromotionMoves(session, pawn);
+
+    expect(moves).toHaveLength(4);
+    const types = moves.map((m) => m.promoteTo).sort();
+    expect(types).toEqual(["bishop", "knight", "queen", "rook"]);
+  });
+});
+
+// ─── Integration: applyPromotion ─────────────────────────────────────────────
+
+describe("promotion-override — integration with applyPromotion", () => {
+  it("PromotionOverride='bishop': promotes to bishop regardless of promoteTo arg", () => {
+    const session = setupSession();
+    const pawn = insertPiece(session, 1, "pawn", "white", 60);
+    session.insert(pawn, "PromotionOverride", "bishop");
+
+    applyPromotion(session, pawn, "queen"); // caller requests queen, override wins
+
+    expect(session.get(pawn, "PieceType")).toBe("bishop");
+  });
+
+  it("PromotionOverride='rook': promotes to rook regardless of default promoteTo", () => {
+    const session = setupSession();
+    const pawn = insertPiece(session, 1, "pawn", "white", 60);
+    session.insert(pawn, "PromotionOverride", "rook");
+
+    applyPromotion(session, pawn); // no promoteTo arg — default is queen, override wins
+
+    expect(session.get(pawn, "PieceType")).toBe("rook");
+  });
+
+  it("PromotionOverride='disabled': falls back to promoteTo arg (pawn stays pawn only if not promoted)", () => {
+    // When override is "disabled", no promotion moves are generated so
+    // applyPromotion shouldn't be called. If it is called anyway, it falls
+    // back to the caller's promoteTo arg (normal behaviour).
+    const session = setupSession();
+    const pawn = insertPiece(session, 1, "pawn", "white", 60);
+    session.insert(pawn, "PromotionOverride", "disabled");
+
+    applyPromotion(session, pawn, "knight");
+
+    expect(session.get(pawn, "PieceType")).toBe("knight");
+  });
+
+  it("no PromotionOverride: applyPromotion uses promoteTo arg normally", () => {
+    const session = setupSession();
+    const pawn = insertPiece(session, 1, "pawn", "white", 60);
+
+    applyPromotion(session, pawn, "rook");
+
+    expect(session.get(pawn, "PieceType")).toBe("rook");
+  });
+});
diff --git a/packages/chess/src/modifiers/descriptors/promotion-override.ts b/packages/chess/src/modifiers/descriptors/promotion-override.ts
new file mode 100644
index 0000000..704ffb6
--- /dev/null
+++ b/packages/chess/src/modifiers/descriptors/promotion-override.ts
@@ -0,0 +1,27 @@
+import { z } from "zod";
+import type { Session, EntityId } from "@paratype/rete";
+import { MODIFIER_REGISTRY } from "../registry.js";
+import type { ModifierDescriptor } from "../types.js";
+
+// Valid override: any standard promotion target, or "disabled" (no promotion).
+// "king" and "pawn" are intentionally excluded — king is not a valid promotion
+// target and pawn would be a no-op / non-sensical promotion.
+const promotionTargetSchema = z.enum(["queen", "rook", "bishop", "knight", "disabled"]);
+type Value = z.infer<typeof promotionTargetSchema>;
+
+export const PROMOTION_OVERRIDE_DESCRIPTOR: ModifierDescriptor<Value> = {
+  id: "promotion-override",
+  attrName: "PromotionOverride",
+  label: "Promotion Override",
+  valueSchema: promotionTargetSchema,
+  stackingRule: "priority-wins",
+  uiForm: "promotion-target",
+  apply(session: Session, pieceId: EntityId, effectiveValue: Value): void {
+    session.insert(pieceId, "PromotionOverride", effectiveValue);
+  },
+  describe(value: Value): string {
+    return value === "disabled" ? "Cannot promote" : `Promotes to ${value}`;
+  },
+};
+
+MODIFIER_REGISTRY.register(PROMOTION_OVERRIDE_DESCRIPTOR);
diff --git a/packages/chess/src/rules/promotion.ts b/packages/chess/src/rules/promotion.ts
index c930652..9c81ac1 100644
--- a/packages/chess/src/rules/promotion.ts
+++ b/packages/chess/src/rules/promotion.ts
@@ -43,7 +43,10 @@ export function isPromotionMove(to: Square, color: PieceColor): boolean {
 /**
  * Enumerate all promotion moves available to `pieceId` from its current
  * square. Returns 4 LegalMove entries per reachable promotion-rank target
- * (one per element of {@link PROMOTION_PIECES}).
+ * (one per element of {@link PROMOTION_PIECES}), unless a PromotionOverride
+ * modifier is active:
+ *   - "disabled" → returns [] (pawn cannot promote)
+ *   - a specific piece type → returns 1 entry per target (only that type)
  *
  * Does not verify that `pieceId` is a pawn — the caller is expected to
  * dispatch on PieceType. Returns [] if the piece has no Position/Color.
@@ -53,6 +56,10 @@ export function getPromotionMoves(session: Session, pieceId: EntityId): LegalMov
   const color = getPieceColor(session, pieceId);
   if (from === null || color === null) return [];
 
+  // Respect PromotionOverride modifier: "disabled" means no promotion moves.
+  const override = session.get(pieceId, "PromotionOverride") as PieceType | "disabled" | undefined;
+  if (override === "disabled") return [];
+
   const candidates: { to: Square; isCapture: boolean }[] = [];
 
   // Single advance to the back rank (must be empty).
@@ -71,9 +78,12 @@ export function getPromotionMoves(session: Session, pieceId: EntityId): LegalMov
   if (candidates.length === 0) return [];
 
   // Fan each candidate target into one LegalMove per promotion piece type.
+  // If PromotionOverride specifies a piece type, offer only that single type.
+  const promotionChoices: readonly PieceType[] =
+    override !== undefined ? [override] : PROMOTION_PIECES;
   const moves: LegalMove[] = [];
   for (const { to, isCapture } of candidates) {
-    for (const promoteTo of PROMOTION_PIECES) {
+    for (const promoteTo of promotionChoices) {
       moves.push({ pieceId, from, to, isCapture, promoteTo });
     }
   }
@@ -85,18 +95,26 @@ export function getPromotionMoves(session: Session, pieceId: EntityId): LegalMov
  * `promoteTo` (defaults to queen). Session.insert has update semantics,
  * so this retracts the old PieceType and inserts the new one atomically.
  *
- * Throws if `promoteTo` is not in {@link PROMOTION_PIECES} (i.e. attempts
- * to promote to pawn or king).
+ * If a PromotionOverride modifier is active on the piece (and is not
+ * "disabled"), the override value takes precedence over `promoteTo`.
+ *
+ * Throws if the final promotion target is not in {@link PROMOTION_PIECES}
+ * (i.e. attempts to promote to pawn or king).
  */
 export function applyPromotion(
   session: Session,
   pieceId: EntityId,
   promoteTo: PieceType = "queen",
 ): void {
-  if (!PROMOTION_PIECES.includes(promoteTo)) {
+  // Respect PromotionOverride modifier: a non-disabled value overrides the
+  // caller's requested target so the piece always becomes the overridden type.
+  const override = session.get(pieceId, "PromotionOverride") as PieceType | "disabled" | undefined;
+  const target = override !== undefined && override !== "disabled" ? override : promoteTo;
+
+  if (!PROMOTION_PIECES.includes(target)) {
     throw new Error(
-      `Invalid promotion target: ${promoteTo}. Cannot promote to king or pawn.`,
+      `Invalid promotion target: ${target}. Cannot promote to king or pawn.`,
     );
   }
-  session.insert(pieceId, "PieceType", promoteTo);
+  session.insert(pieceId, "PieceType", target);
 }