diff --git a/README.md b/README.md
index 07faade..b1c39e3 100644
--- a/README.md
+++ b/README.md
@@ -82,7 +82,8 @@ Rounds moyens : 6.0
 
 ```
 usage: pf1e-sim [-h] --map MAP [--side NAME [FILE ...]] [--runs RUNS]
-                [--seed SEED] [--round-cap ROUND_CAP]
+                [--seed SEED] [--round-cap ROUND_CAP] [--transcript]
+                [--simple-monster-death]
 ```
 
 | Option | Rôle | Défaut |
@@ -92,6 +93,8 @@ usage: pf1e-sim [-h] --map MAP [--side NAME [FILE ...]] [--runs RUNS]
 | `--runs RUNS` | Nombre de combats simulés | `1000` |
 | `--seed SEED` | Graine du générateur aléatoire | `1` |
 | `--round-cap ROUND_CAP` | Plafond de rounds par combat (au-delà, combat nul) | `100` |
+| `--transcript` | Imprimer le déroulé du premier combat avant le rapport | désactivé |
+| `--simple-monster-death` | Mort simplifiée des monstres : `hp ≤ 0` au lieu de `hp ≤ -CON` (les PJ ne sont jamais affectés) | désactivé |
 
 Codes de sortie :
 
@@ -294,6 +297,22 @@ Règles modélisées :
   La mort survient quand les pv négatifs atteignent le score de CON
   (`hp ≤ -CON`) — conformance P2 : la règle du −10 de D&D 3.5 n'existe pas
   en PF1e et n'est plus modélisée.
+- Mort simplifiée des monstres (option `--simple-monster-death`, défaut
+  désactivé) : quand l'option est présente dans la commande, un **monstre**
+  meurt dès `hp ≤ 0` — ni bande d'invalidité à 0 pv, ni bande d'agonie entre
+  0 et `-CON`. Les **personnages joueurs ne sont jamais affectés**, quel que
+  soit le réglage : ils gardent la règle PF1e complète (`hp ≤ -CON` pour
+  mourir, invalidité à 0 pv, agonie et stabilisation en dessous). La
+  distinction monstre/PJ repose sur une seule marque fiable issue du
+  chargeur : le champ `source` des JSON de PJ pointe vers la fiche Foundry
+  d'origine sous `fiches_personnages/` (convention documentée plus bas),
+  alors que les JSON de monstres portent des sources « Bestiary », « summon
+  monster » ou « bestiary » ; le nom de camp (`--side`) ne peut pas servir
+  de critère puisqu'il est choisi par l'utilisateur et que la carte d'exemple
+  oppose des monstres déployés côté `players`. Sans l'option, le comportement
+  du moteur est bit-identique à celui d'aujourd'hui (transcripts dorés
+  intacts). Équivalent Python : `run_encounter(..., monsters_die_at_zero=True)`
+  et `CombatEngine(..., monsters_die_at_zero=True)`.
 - Invalide (conformance P2, CRB « Effects of Death ») : à `hp = 0`
   exactement, une créature est **invalide** — elle reste active mais
   **staggered** (une action de mouvement OU une action standard par tour, pas
diff --git a/src/pf1e_simulator/cli.py b/src/pf1e_simulator/cli.py
index 353f935..959f114 100644
--- a/src/pf1e_simulator/cli.py
+++ b/src/pf1e_simulator/cli.py
@@ -105,6 +105,14 @@ def main(argv: list[str] | None = None) -> int:
         action="store_true",
         help="print the turn-by-turn log of the first battle before the report",
     )
+    parser.add_argument(
+        "--simple-monster-death",
+        action="store_true",
+        help=(
+            "monsters die at hp <= 0 instead of the PF1e hp <= -CON rule "
+            "(player characters are never affected)"
+        ),
+    )
     args = parser.parse_args(argv)
     if not args.side:
         parser.error("at least one --side is required")
@@ -124,6 +132,7 @@ def main(argv: list[str] | None = None) -> int:
             seed=args.seed,
             spell_registry=registry,
             capture_first_transcript=args.transcript,
+            monsters_die_at_zero=args.simple_monster_death,
         )
     except ValueError as exc:
         print(f"pf1e-sim: {exc}", file=sys.stderr)
diff --git a/src/pf1e_simulator/combat.py b/src/pf1e_simulator/combat.py
index 217d623..8d2bce3 100644
--- a/src/pf1e_simulator/combat.py
+++ b/src/pf1e_simulator/combat.py
@@ -40,6 +40,9 @@ Phase 0 documented deviations from PF1e (conventions):
   has no -10 rule. At exactly 0 hp a living creature is disabled: active,
   staggered (one move OR standard action per round) at half speed, and a
   non-movement action costs 1 hp at its end (hp -> -1, dying).
+  Optional rule (``monsters_die_at_zero``, CLI ``--simple-monster-death``):
+  monster combatants die at hp <= 0 instead — player characters are never
+  affected and the default (flag off) is the PF1e rule above, bit-identical.
 - Initiative ties: higher initiative_mod first, then list order (no re-roll).
 - Movement: a move action travels up to the combatant's speed in cells along
   the true shortest path (Dijkstra cost field from the target, 5-10-5
@@ -426,6 +429,23 @@ class CombatantStats:
     damage_taken: int = 0
 
 
+_PC_SOURCE_PREFIX = "fiches_personnages/"
+
+
+def _is_pc_combatant(combatant: Combatant) -> bool:
+    """True for player characters, False for monsters (X5 classification).
+
+    The unified loader records each combatant's origin in ``source``: every
+    PC JSON (``data/pcs/*.json``) points at its Foundry sheet under
+    ``fiches_personnages/`` (README convention), while monster JSONs carry
+    bestiary/summon sources. ``side`` is a user-chosen faction name and
+    ``cr``/``xp`` are absent from some monster files, so ``source`` is the
+    only robust per-combatant marker that survives loading without a schema
+    change.
+    """
+    return combatant.source.startswith(_PC_SOURCE_PREFIX)
+
+
 @dataclass
 class CombatantState:
     """Mutable runtime state of one combatant on the grid."""
@@ -459,6 +479,10 @@ class CombatantState:
     # Dying & stabilization (not in the frozen data model): the hp at which
     # this combatant stabilized while dying; None = not stabilized.
     stabilized_hp: int | None = None
+    # Simple monster death (X5, not in the frozen data model): set by the
+    # engine when ``monsters_die_at_zero`` is on, for monster combatants only
+    # — the combatant dies at hp <= 0 instead of the PF1e hp <= -CON rule.
+    dies_at_zero: bool = False
     # Action feedback (not in the frozen data model): the ActionResults of the
     # PREVIOUS turn, assigned at the end of each turn so the Observation built
     # at the next policy invocation can expose them.
@@ -534,8 +558,10 @@ class CombatantState:
     def active(self) -> bool:
         """PF1e: hp > 0 acts normally; hp == 0 is DISABLED (CRB, Effects of
         Death: a living creature at exactly 0 hp can still take a single move
-        or standard action), so it remains active. hp < 0 is dying/dead."""
-        return self.hp >= 0
+        or standard action), so it remains active. hp < 0 is dying/dead.
+        Under the simple monster-death rule (``dies_at_zero``) hp <= 0 is
+        dead, so the disabled band never applies."""
+        return self.hp >= 0 and not self.dead
 
     @property
     def dead(self) -> bool:
@@ -543,7 +569,10 @@ class CombatantState:
 
     @property
     def death_threshold(self) -> int:
-        """PF1e (CRB): death when negative hp reaches the CON score (no -10 rule)."""
+        """PF1e (CRB): death when negative hp reaches the CON score (no -10 rule).
+        The optional simple monster-death rule raises the threshold to 0."""
+        if self.dies_at_zero:
+            return 0
         return -self.combatant.abilities.con_score
 
 
@@ -874,6 +903,7 @@ class CombatEngine:
         llm_policy: LLMPolicy | None = None,
         spell_registry: dict[str, SpellSpec] | None = None,
         reaction_policy: ReactionPolicy | None = None,
+        monsters_die_at_zero: bool = False,
     ) -> None:
         if policy is not None and llm_policy is not None:
             msg = "policy and llm_policy are mutually exclusive"
@@ -888,6 +918,10 @@ class CombatEngine:
             self._policy = policy if policy is not None else default_policy
         self._spell_registry = spell_registry or {}
         self._reaction_policy = reaction_policy
+        self._monsters_die_at_zero = monsters_die_at_zero
+        if monsters_die_at_zero:
+            for st in states:
+                self._apply_simple_monster_death(st)
         self._in_reaction = False
         self._transcript: list[str] = []
         self._stats: dict[str, _LiveStats] = {s.combatant.id: _LiveStats() for s in states}
@@ -911,6 +945,12 @@ class CombatEngine:
         """The spell registry used for spell lookups."""
         return self._spell_registry
 
+    def _apply_simple_monster_death(self, state: CombatantState) -> None:
+        """Opt-in X5 rule: with ``monsters_die_at_zero``, monster combatants
+        die at hp <= 0 (no dying/disabled band); PCs are never marked."""
+        if self._monsters_die_at_zero and not _is_pc_combatant(state.combatant):
+            state.dies_at_zero = True
+
     def _llm_adapter(self, llm_policy: LLMPolicy) -> Policy:
         """Wrap an ``LLMPolicy`` into a ``Policy``.
 
@@ -5165,6 +5205,7 @@ class CombatEngine:
         # Set expiration
         summoned_state.summon_duration = effect.duration_rounds
         summoned_state.summon_caster_id = state.combatant.id
+        self._apply_simple_monster_death(summoned_state)
 
         self._stats[summoned_state.combatant.id] = _LiveStats()
         self._pending_summons.append(summoned_state)
diff --git a/src/pf1e_simulator/runner.py b/src/pf1e_simulator/runner.py
index 19d4967..d0f442b 100644
--- a/src/pf1e_simulator/runner.py
+++ b/src/pf1e_simulator/runner.py
@@ -169,6 +169,7 @@ def run_encounter(
     policy: Policy | None = None,
     spell_registry: dict[str, SpellSpec] | None = None,
     capture_first_transcript: bool = False,
+    monsters_die_at_zero: bool = False,
 ) -> EncounterReport:
     """Run `runs` battles (one SeededRng per run) and aggregate balance metrics.
 
@@ -177,6 +178,10 @@ def run_encounter(
 
     When ``capture_first_transcript`` is True, the turn-by-turn log of the
     first battle (``seed + 0``) is stored in ``report.transcript``.
+
+    ``monsters_die_at_zero`` enables the optional simple monster-death rule
+    (CLI ``--simple-monster-death``): monsters die at hp <= 0; PCs keep the
+    PF1e hp <= -CON rule. Default False keeps behavior bit-identical.
     """
     if runs <= 0:
         msg = "runs must be positive"
@@ -202,6 +207,7 @@ def run_encounter(
             round_cap=spec.round_cap,
             policy=policy,
             spell_registry=spell_registry,
+            monsters_die_at_zero=monsters_die_at_zero,
         ).run()
         if capture_first_transcript and index == 0:
             transcript = result.transcript
diff --git a/tests/test_conformance_simple_monster_death.py b/tests/test_conformance_simple_monster_death.py
new file mode 100644
index 0000000..04fcc68
--- /dev/null
+++ b/tests/test_conformance_simple_monster_death.py
@@ -0,0 +1,286 @@
+"""Conformance X5: optional simple monster death (monsters die at hp <= 0).
+
+PF1e death is ``hp <= -CON`` (CRB, Effects of Death) with a disabled band at
+exactly 0 hp and a dying band below 0. The opt-in ``monsters_die_at_zero``
+engine option (CLI ``--simple-monster-death``) raises the death threshold to
+0 for MONSTER combatants only: a monster at hp <= 0 is dead outright (no
+dying, no disabled band). Player characters are NEVER affected — they are
+identified by the loader convention that a PC's ``source`` records its
+Foundry sheet path under ``fiches_personnages/`` (README, "Fiches de
+personnages"); monsters carry bestiary/summon sources. With the option off,
+behavior is bit-identical to the PF1e rule (goldens frozen).
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import TYPE_CHECKING
+
+import pytest
+
+if TYPE_CHECKING:
+    from pf1e_simulator.models import Combatant
+
+from pf1e_simulator import cli
+from pf1e_simulator.combat import CombatantState, CombatEngine, Policy
+from pf1e_simulator.grid import Grid
+from pf1e_simulator.loaders.combatant import load_combatant
+from pf1e_simulator.map import MapSpec, TerrainType, load_map
+from pf1e_simulator.rng import RngExhaustedError, ScriptedRng
+from pf1e_simulator.runner import (
+    CombatantAttrition,
+    EncounterReport,
+    EncounterSpec,
+    Side,
+    build_states,
+    run_encounter,
+)
+from pf1e_simulator.spells import SpellSpec, load_spell_registry
+from tests.test_combat import make_combatant
+from tests.test_pc_combat_golden import _build_queue
+
+ROOT = Path(__file__).resolve().parents[1]
+DATA_DIR = ROOT / "data"
+PCS_DIR = DATA_DIR / "pcs"
+MAP = DATA_DIR / "maps" / "sample_arena.yaml"
+GOBLIN = DATA_DIR / "monsters" / "goblin.json"
+ORC = DATA_DIR / "monsters" / "orc.json"
+
+_MONSTER_SOURCE = "Bestiary > Goblin"
+_PC_SOURCE = "fiches_personnages/tammara_sheet.json"
+
+
+def _monster(cid: str = "goblin", con: int = 12) -> Combatant:
+    return make_combatant(cid, con=con).model_copy(update={"source": _MONSTER_SOURCE})
+
+
+def _pc(cid: str = "hero", con: int = 12) -> Combatant:
+    return make_combatant(cid, con=con).model_copy(update={"source": _PC_SOURCE})
+
+
+def _state(combatant: Combatant, side: str, hp: int) -> CombatantState:
+    return CombatantState(combatant=combatant, side=side, pos=(1, 1), hp=hp)
+
+
+def _grid(width: int = 8) -> Grid:
+    legend = {".": TerrainType(type="floor", move_cost=1)}
+    spec = MapSpec(name="test", terrain=tuple(["." * width] * width), legend=legend)
+    return Grid.from_spec(spec)
+
+
+def _engine(
+    states: list[CombatantState], *, monsters_die_at_zero: bool = False
+) -> CombatEngine:
+    return CombatEngine(
+        ScriptedRng([1] * 50),
+        _grid(),
+        states,
+        monsters_die_at_zero=monsters_die_at_zero,
+    )
+
+
+# ── (a) monster at hp 0: dead with the flag, disabled band without ──────────
+
+
+def test_monster_at_zero_hp_is_dead_with_flag_on() -> None:
+    st = _state(_monster(), "monsters", hp=0)
+    engine = _engine([st], monsters_die_at_zero=True)
+    assert engine.states[0].dies_at_zero is True
+    assert st.dead is True
+    assert st.active is False
+
+
+def test_monster_at_zero_hp_keeps_disabled_band_with_flag_off() -> None:
+    st = _state(_monster(), "monsters", hp=0)
+    _engine([st])
+    assert st.dies_at_zero is False
+    assert st.dead is False
+    assert st.active is True  # CRB "Effects of Death": disabled, still acting
+
+
+# ── (b) monster at/below -CON: dead in both modes; band only dies with flag ─
+
+
+def test_monster_dead_at_minus_con_in_both_modes() -> None:
+    down = _state(_monster(con=12), "monsters", hp=-12)
+    up = _state(_monster(con=12), "monsters", hp=-12)
+    _engine([down])
+    _engine([up], monsters_die_at_zero=True)
+    assert down.dead is True
+    assert up.dead is True
+
+
+def test_monster_dying_band_is_dead_only_with_flag_on() -> None:
+    off = _state(_monster(con=12), "monsters", hp=-1)
+    on = _state(_monster(con=12), "monsters", hp=-1)
+    _engine([off])
+    _engine([on], monsters_die_at_zero=True)
+    assert off.dead is False  # PF1e dying: -1 > -CON
+    assert on.dead is True
+
+
+# ── (c) PCs are never affected by the rule ───────────────────────────────────
+
+
+def test_pc_at_zero_hp_is_never_dead_even_with_flag_on() -> None:
+    st = _state(_pc(), "players", hp=0)
+    _engine([st], monsters_die_at_zero=True)
+    assert st.dies_at_zero is False
+    assert st.dead is False
+    assert st.active is True  # disabled band preserved for PCs
+
+
+def test_pc_death_still_requires_minus_con_with_flag_on() -> None:
+    dying = _state(_pc(con=12), "players", hp=-1)
+    dead = _state(_pc(con=12), "players", hp=-12)
+    _engine([dying, dead], monsters_die_at_zero=True)
+    assert dying.dies_at_zero is False
+    assert dying.dead is False  # PC dying band untouched
+    assert dead.dead is True  # PF1e hp <= -CON still kills the PC
+
+
+# ── classification + dying machinery integration ─────────────────────────────
+
+
+def test_flag_off_marks_no_state() -> None:
+    m = _state(_monster(), "monsters", hp=6)
+    p = _state(_pc(), "players", hp=6)
+    _engine([m, p])
+    assert m.dies_at_zero is False
+    assert p.dies_at_zero is False
+
+
+def test_foundry_sourced_combatant_never_marked() -> None:
+    """The classification helper keys on the ``fiches_personnages/`` source."""
+    st = _state(_pc(), "players", hp=6)
+    _engine([st], monsters_die_at_zero=True)
+    assert st.dies_at_zero is False
+
+
+def test_summon_style_source_is_a_monster() -> None:
+    summoned = make_combatant("wolf").model_copy(update={"source": "summon monster II"})
+    st = _state(summoned, "players", hp=6)
+    engine = _engine([st], monsters_die_at_zero=True)
+    engine._apply_simple_monster_death(st)  # the hook used at the summon site
+    assert st.dies_at_zero is True
+
+
+def test_dying_stabilization_check_skipped_for_dead_monster() -> None:
+    """With the flag on, a monster below 0 hp is dead: no CON check, no RNG."""
+    st = _state(_monster(con=12), "monsters", hp=-2)
+    engine = CombatEngine(ScriptedRng([]), _grid(), [st], monsters_die_at_zero=True)
+    engine._process_dying(st)  # would raise RngExhaustedError if it rolled
+
+    off = _state(_monster(con=12), "monsters", hp=-2)
+    off_engine = CombatEngine(ScriptedRng([]), _grid(), [off])
+    with pytest.raises(RngExhaustedError):
+        off_engine._process_dying(off)  # dying CON check consumes the d20
+
+
+# ── (d) flag OFF end-to-end: bit-identical transcripts when no monster
+#    enters the hp 0..-CON band (tammara vs lich: the PC bleeds, the lich does not)
+
+
+def _golden_harness_engine(*, monsters_die_at_zero: bool) -> CombatEngine:
+    pc = load_combatant(PCS_DIR / "tammara.json")
+    monster = load_combatant(DATA_DIR / "monsters" / "lich.json")
+    registry = load_spell_registry(DATA_DIR / "spells")
+    pc_state = CombatantState(combatant=pc, side="players", pos=(0, 0), hp=pc.hp_max)
+    monster_state = CombatantState(
+        combatant=monster, side="monsters", pos=(10, 10), hp=monster.hp_max
+    )
+    return CombatEngine(
+        ScriptedRng(list(_build_queue())),
+        _grid(width=20),
+        [pc_state, monster_state],
+        round_cap=10,
+        spell_registry=registry,
+        monsters_die_at_zero=monsters_die_at_zero,
+    )
+
+
+def test_flag_off_equivalence_when_band_never_entered() -> None:
+    plain = _golden_harness_engine(monsters_die_at_zero=False)
+    result_plain = plain.run()
+    simple = _golden_harness_engine(monsters_die_at_zero=True)
+    result_simple = simple.run()
+    assert result_plain.transcript == result_simple.transcript
+    assert result_plain.winner == result_simple.winner == "monsters"
+    tammara = plain.states[0]
+    assert tammara.hp < 0  # the PC bled into the dying band…
+    assert tammara.dies_at_zero is False  # …without dying at 0, flag or not
+    assert tammara.dead is False
+
+
+# ── runner + CLI wiring ───────────────────────────────────────────────────────
+
+
+def _spec() -> EncounterSpec:
+    goblins = tuple(load_combatant(GOBLIN) for _ in range(3))
+    orcs = tuple(load_combatant(ORC) for _ in range(2))
+    return EncounterSpec(
+        map=load_map(MAP),
+        sides=(
+            Side(name="players", combatants=goblins, zone="A"),
+            Side(name="monsters", combatants=orcs, zone="B"),
+        ),
+        round_cap=100,
+    )
+
+
+def test_run_encounter_accepts_the_flag() -> None:
+    report = run_encounter(_spec(), runs=5, seed=1, monsters_die_at_zero=True)
+    assert report.runs == 5
+    assert sum(report.wins.values()) + report.draws == 5
+    states = build_states(_spec())
+    assert all(not s.dies_at_zero for s in states)  # build_states stays neutral
+
+
+def test_cli_help_lists_the_option(capsys: pytest.CaptureFixture[str]) -> None:
+    with pytest.raises(SystemExit) as excinfo:
+        cli.main(["--help"])
+    assert excinfo.value.code == 0
+    assert "--simple-monster-death" in capsys.readouterr().out
+
+
+def test_cli_wires_the_flag_to_the_runner(
+    monkeypatch: pytest.MonkeyPatch,
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    seen: list[bool] = []
+
+    def spy(
+        spec: EncounterSpec,
+        runs: int,
+        seed: int,
+        *,
+        policy: Policy | None = None,
+        spell_registry: dict[str, SpellSpec] | None = None,
+        capture_first_transcript: bool = False,
+        monsters_die_at_zero: bool = False,
+    ) -> EncounterReport:
+        seen.append(monsters_die_at_zero)
+        return EncounterReport(
+            runs=runs,
+            seed=seed,
+            wins={side.name: runs for side in spec.sides},
+            draws=0,
+            avg_rounds=1.0,
+            attrition={
+                combatant.id: CombatantAttrition(0.0, 0.0, 0.0, 0.0)
+                for side in spec.sides
+                for combatant in side.combatants
+            },
+        )
+
+    monkeypatch.setattr(cli, "run_encounter", spy)
+    base = [
+        "--map", str(MAP),
+        "--side", "players", str(GOBLIN),
+        "--side", "monsters", str(ORC),
+        "--runs", "5",
+    ]
+    assert cli.main(base) == 0
+    assert cli.main([*base, "--simple-monster-death"]) == 0
+    assert seen == [False, True]
+    assert "Rapport d'équilibrage" in capsys.readouterr().out