Combat: implement stateful monster ability effects

Slice 3 of the bestiary SRD upgrade: the monster abilities that need
per-fight state (evade, block, advantage, retaliate, regenerate,
survive_at_1, stat_drain, debuff, max_hp_drain). applyAbility arms
combatState flags that the shared resolution primitives read, so both
the auto-resolve and turn-based engines honor them; the turn-based
engine round-trips them through CombatStatuses so a suspended fight
resumes from exact mid-state. New branches are guarded by zero-valued
state so the auto-resolve characterization golden is untouched.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/plugin/bestiary_srd_test.go

@@ -144,6 +144,94 @@ func TestApplyAbility_Slice2Effects(t *testing.T) {
 	}
 }
 
+// TestApplyAbility_Slice3Effects covers the stateful monster-ability effects:
+// applyAbility arms a combatState flag/counter (and emits an announcement for
+// all but evade), and the shared resolution primitives read that state.
+func TestApplyAbility_Slice3Effects(t *testing.T) {
+	newState := func(playerHP, enemyHP int) (*combatState, Combatant, Combatant) {
+		st := &combatState{
+			playerHP: playerHP, enemyHP: enemyHP, round: 1,
+			rng: rand.New(rand.NewPCG(9, 9)),
+		}
+		return st, basePlayer(), baseEnemy()
+	}
+	phase := &turnCombatPhase
+	res := &CombatResult{}
+
+	// Each effect arms its combatState field and (except evade) announces itself.
+	st, pl, en := newState(100, 60)
+	en.Ability = &MonsterAbility{Name: "Scurry", Effect: "evade"}
+	applyAbility(st, &pl, &en, phase, res)
+	if !st.enemyEvadeNext || len(st.events) != 0 {
+		t.Errorf("evade: want enemyEvadeNext set and no event, got flag=%v events=%d", st.enemyEvadeNext, len(st.events))
+	}
+
+	armChecks := []struct {
+		effect string
+		armed  func(*combatState) bool
+	}{
+		{"block", func(s *combatState) bool { return s.enemyBlockUp }},
+		{"advantage", func(s *combatState) bool { return s.enemyAdvantage }},
+		{"retaliate", func(s *combatState) bool { return s.enemyRetaliateFrac > 0 }},
+		{"regenerate", func(s *combatState) bool { return s.enemyRegen > 0 }},
+		{"survive_at_1", func(s *combatState) bool { return s.enemySurviveArmed }},
+		{"stat_drain", func(s *combatState) bool { return s.playerAtkDrain > 0 }},
+		{"debuff", func(s *combatState) bool { return s.playerACDebuff > 0 }},
+	}
+	for _, c := range armChecks {
+		st, pl, en := newState(100, 60)
+		en.Ability = &MonsterAbility{Name: "Test " + c.effect, Effect: c.effect}
+		if applyAbility(st, &pl, &en, phase, res) {
+			t.Errorf("%s: should not down a full-HP player", c.effect)
+		}
+		if !c.armed(st) {
+			t.Errorf("%s: combatState flag not armed", c.effect)
+		}
+		if len(st.events) != 1 {
+			t.Errorf("%s: want one announcement event, got %d", c.effect, len(st.events))
+		}
+	}
+
+	// max_hp_drain lowers effective MaxHP and deals that much immediate damage.
+	stD, plD, enD := newState(100, 60)
+	enD.Ability = &MonsterAbility{Name: "Corrupting Touch", Effect: "max_hp_drain"}
+	applyAbility(stD, &plD, &enD, phase, res)
+	if stD.maxHPDrain <= 0 || stD.playerHP != 100-stD.maxHPDrain {
+		t.Errorf("max_hp_drain: drain=%d playerHP=%d, want playerHP = 100-drain", stD.maxHPDrain, stD.playerHP)
+	}
+
+	// enemyDown lets survive_at_1 cheat death exactly once.
+	stS := &combatState{enemyHP: 0, enemySurviveArmed: true}
+	if enemyDown(stS, "Duel") {
+		t.Error("survive_at_1: armed enemy at 0 HP should not be down")
+	}
+	if stS.enemyHP != 1 || stS.enemySurviveArmed {
+		t.Errorf("survive_at_1: want enemyHP=1 and flag cleared, got hp=%d armed=%v", stS.enemyHP, stS.enemySurviveArmed)
+	}
+	stS.enemyHP = 0
+	if !enemyDown(stS, "Duel") {
+		t.Error("survive_at_1: second drop to 0 should be lethal (one-shot spent)")
+	}
+
+	// evade is consumed by the next player weapon attack — a guaranteed miss.
+	stE, plE, enE := newState(100, 60)
+	stE.enemyEvadeNext = true
+	if resolvePlayerAttack(stE, &plE, &enE, phase, res) {
+		t.Error("evade: a whiffed attack should not end the fight")
+	}
+	if stE.enemyEvadeNext || stE.enemyHP != 60 {
+		t.Errorf("evade: want flag cleared and enemyHP unchanged, got flag=%v hp=%d", stE.enemyEvadeNext, stE.enemyHP)
+	}
+
+	// retaliate reflects a fraction of every player hit back at the player.
+	stR, plR, enR := newState(100, 60)
+	stR.enemyRetaliateFrac = 0.5
+	resolvePlayerAttack(stR, &plR, &enR, phase, res)
+	if stR.playerHP >= 100 {
+		t.Errorf("retaliate: player HP = %d, want < 100 (reflected damage)", stR.playerHP)
+	}
+}
+
 // TestTurnEngine_Multiattack drives a single enemy_turn and confirms a
 // registered multiattack creature resolves one attack roll per profile entry,
 // while an unregistered creature still resolves exactly one.

internal/plugin/combat_bridge.go

@@ -469,7 +469,7 @@ func combatDegradation(result CombatResult, equip map[EquipmentSlot]*AdvEquipmen
 			damage[SlotHelmet] += 1 + rand.IntN(2)
 		case ev.Actor == "enemy" && ev.Action == "cleave":
 			damage[SlotArmor] += 2 + rand.IntN(3)
-		case ev.Actor == "enemy" && (ev.Action == "bonus_damage" || ev.Action == "aoe" || ev.Action == "execute"):
+		case ev.Actor == "enemy" && (ev.Action == "bonus_damage" || ev.Action == "aoe" || ev.Action == "execute" || ev.Action == "retaliate" || ev.Action == "max_hp_drain"):
 			damage[SlotArmor] += 1 + rand.IntN(2)
 		case ev.Actor == "enemy" && ev.Action == "lifesteal":
 			damage[SlotArmor] += 1 + rand.IntN(2)

internal/plugin/combat_engine.go

@@ -200,8 +200,11 @@ type MonsterAbility struct {
 	// Effect — the mechanic the ability applies. Implemented in applyAbility:
 	// stand-in attacks (cleave, lifesteal); riders on the normal attack (poison,
 	// enrage, armor_break, stun, bonus_damage, aoe, aoe_fire, death_aoe, execute,
-	// self_heal); flavor-only placeholders pending per-fight state (spell_resist,
+	// self_heal, max_hp_drain); stateful effects armed here and read by the
-	// reveal_action, fear_immune, ally_buff). Anything else is a silent no-op.
+	// shared resolution primitives (evade, block, advantage, retaliate,
+	// regenerate, survive_at_1, stat_drain, debuff); flavor-only placeholders
+	// (spell_resist, reveal_action, fear_immune, ally_buff). Anything else is a
+	// silent no-op.
 	Effect string
 }
 
@@ -284,6 +287,20 @@ type combatState struct {
 	// Phase 10 SUB2b — Abjuration Arcane Ward HP buffer.
 	arcaneWardHP int
 
+	// Phase 13 bestiary slice 3 — stateful monster-ability effects. Each is
+	// armed by applyAbility and read by the shared resolution primitives, so
+	// both engines honour them; the turn-based engine additionally round-trips
+	// them through CombatStatuses so they survive a suspend/resume.
+	enemyEvadeNext     bool    // evade: next player weapon attack auto-misses
+	enemyBlockUp       bool    // block: enemy holds a parry stance (~50% block on player hits)
+	enemyAdvantage     bool    // advantage: enemy rolls its attacks with advantage
+	enemyRetaliateFrac float64 // retaliate: fraction of a player hit reflected back
+	enemyRegen         int     // regenerate: enemy heals this much each round end
+	enemySurviveArmed  bool    // survive_at_1: enemy cheats death once, dropping to 1 HP
+	playerAtkDrain     int     // stat_drain: flat reduction to the player's hit damage
+	playerACDebuff     int     // debuff: flat reduction to the player's effective AC
+	maxHPDrain         int     // max_hp_drain: reduction to the player's effective MaxHP
+
 	round  int
 	events []CombatEvent
 
@@ -557,7 +574,7 @@ func simulateRound(st *combatState, player, enemy *Combatant, phase *CombatPhase
 			Round: st.round, Phase: phaseName, Actor: "pet", Action: "pet_attack",
 			Damage: petDmg, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
 		})
-		if st.enemyHP <= 0 {
+		if enemyDown(st, phaseName) {
 			return true
 		}
 	}
@@ -565,7 +582,7 @@ func simulateRound(st *combatState, player, enemy *Combatant, phase *CombatPhase
 	// Misty heal
 	if player.Mods.MistyHealProc > 0 && st.randFloat() < player.Mods.MistyHealProc {
 		healAmt := player.Mods.MistyHealAmt
-		st.playerHP = min(player.Stats.MaxHP, st.playerHP+healAmt)
+		st.playerHP = min(effPlayerMaxHP(player, st), st.playerHP+healAmt)
 		result.MistyHealed = true
 		st.events = append(st.events, CombatEvent{
 			Round: st.round, Phase: phaseName, Actor: "npc", Action: "misty_heal",
@@ -585,13 +602,23 @@ func simulateRound(st *combatState, player, enemy *Combatant, phase *CombatPhase
 		st.playerHP > 0 && st.playerHP*5 < player.Stats.MaxHP*3 {
 		st.healChargesLeft--
 		healAmt := player.Mods.HealItem
-		st.playerHP = min(player.Stats.MaxHP, st.playerHP+healAmt)
+		st.playerHP = min(effPlayerMaxHP(player, st), st.playerHP+healAmt)
 		st.events = append(st.events, CombatEvent{
 			Round: st.round, Phase: phaseName, Actor: "consumable", Action: "heal_item",
 			Damage: healAmt, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
 		})
 	}
 
+	// Regenerate (monster ability): the enemy knits its wounds at the close of
+	// every round once the ability has armed st.enemyRegen.
+	if st.enemyRegen > 0 && st.enemyHP > 0 && st.enemyHP < enemy.Stats.MaxHP {
+		st.enemyHP = min(enemy.Stats.MaxHP, st.enemyHP+st.enemyRegen)
+		st.events = append(st.events, CombatEvent{
+			Round: st.round, Phase: phaseName, Actor: "enemy", Action: "regen_tick",
+			Damage: st.enemyRegen, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
+		})
+	}
+
 	return false
 }
 
@@ -613,6 +640,17 @@ func resolvePlayerAttack(st *combatState, player, enemy *Combatant, phase *Comba
 		return false
 	}
 
+	// Evade (monster ability): the enemy slipped out of reach — this swing
+	// finds nothing. Consumed here, armed by applyAbility's "evade" case.
+	if st.enemyEvadeNext {
+		st.enemyEvadeNext = false
+		st.events = append(st.events, CombatEvent{
+			Round: st.round, Phase: phaseName, Actor: "enemy", Action: "evade",
+			PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
+		})
+		return false
+	}
+
 	// Orc Rage: trigger on the first attack after dropping below 50% HP.
 	// Use HP*2 < MaxHP rather than HP < MaxHP/2 so the threshold is exact
 	// regardless of MaxHP parity (avoids per-character drift on odd MaxHP).
@@ -701,7 +739,19 @@ func resolvePlayerAttack(st *combatState, player, enemy *Combatant, phase *Comba
 			enemy.Stats.Defense, phase.DefenseWeight, enemy.Mods.DamageReduct)
 	}
 
+	// Stat drain (monster ability): the player's strength has been sapped — a
+	// flat, accumulating reduction to the damage every hit deals.
+	if st.playerAtkDrain > 0 {
+		dmg = max(1, dmg-st.playerAtkDrain)
+	}
+
 	blocked := enemy.Stats.BlockRate > 0 && st.randFloat() < enemy.Stats.BlockRate
+	// Parry stance (monster ability): an enemy holding a block stance rolls a
+	// further ~50% chance to halve the hit. Guarded by enemyBlockUp so the
+	// extra randFloat is only drawn once the ability has actually fired.
+	if !blocked && st.enemyBlockUp && st.randFloat() < 0.5 {
+		blocked = true
+	}
 	if blocked {
 		dmg = max(1, dmg/2)
 	}
@@ -714,7 +764,23 @@ func resolvePlayerAttack(st *combatState, player, enemy *Combatant, phase *Comba
 		Damage: dmg, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
 		Roll: roll, RollAgainst: enemy.Stats.AC, Desc: desc,
 	})
-	return st.enemyHP <= 0
+
+	// Retaliate (monster ability): a damaging aura reflects a fraction of the
+	// hit straight back. Resolved per player hit; can drop the player, so this
+	// path can return true with the enemy still standing — callers disambiguate
+	// the outcome by inspecting HP (see stepPlayerTurn).
+	if st.enemyRetaliateFrac > 0 {
+		retal := max(1, int(float64(dmg)*st.enemyRetaliateFrac))
+		st.playerHP = max(0, st.playerHP-retal)
+		st.events = append(st.events, CombatEvent{
+			Round: st.round, Phase: phaseName, Actor: "enemy", Action: "retaliate",
+			Damage: retal, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
+		})
+		if st.playerHP <= 0 && !trySave(st, player, phaseName) {
+			return true
+		}
+	}
+	return enemyDown(st, phaseName)
 }
 
 // resolveEnemyAttack — enemy rolls d20 + AttackBonus vs player AC.
@@ -744,11 +810,27 @@ func resolveEnemyAttack(st *combatState, player, enemy *Combatant, phase *Combat
 	}
 
 	roll := 1 + st.roll(20)
+	// Advantage (monster ability): the enemy rolls a second d20 and keeps the
+	// better. Guarded by enemyAdvantage so the extra roll is only drawn once the
+	// ability has fired.
+	if st.enemyAdvantage {
+		if alt := 1 + st.roll(20); alt > roll {
+			roll = alt
+		}
+	}
 	isFumble := roll == 1
 	isNat20 := roll == 20
 	total := roll + effectiveAttackBonus(enemy.Stats)
 
-	if !attackConnects(roll, total, player.Stats.AC, 20) {
+	// Debuff (monster ability): a flat, accumulating reduction to the player's
+	// effective AC, so the enemy's attacks land more often. Floored at 1.
+	// Guarded so an undebuffed player's AC passes through untouched.
+	targetAC := player.Stats.AC
+	if st.playerACDebuff > 0 {
+		targetAC = max(1, player.Stats.AC-st.playerACDebuff)
+	}
+
+	if !attackConnects(roll, total, targetAC, 20) {
 		desc := ""
 		if isFumble {
 			desc = "fumble"
@@ -756,7 +838,7 @@ func resolveEnemyAttack(st *combatState, player, enemy *Combatant, phase *Combat
 		st.events = append(st.events, CombatEvent{
 			Round: st.round, Phase: phaseName, Actor: "enemy", Action: "miss",
 			PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
-			Roll: roll, RollAgainst: player.Stats.AC, Desc: desc,
+			Roll: roll, RollAgainst: targetAC, Desc: desc,
 		})
 		return false
 	}
@@ -831,7 +913,7 @@ func resolveEnemyAttack(st *combatState, player, enemy *Combatant, phase *Combat
 	st.events = append(st.events, CombatEvent{
 		Round: st.round, Phase: phaseName, Actor: "enemy", Action: action,
 		Damage: dmg, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
-		Roll: roll, RollAgainst: player.Stats.AC,
+		Roll: roll, RollAgainst: targetAC,
 	})
 
 	if st.reflectFrac > 0 {
@@ -842,7 +924,7 @@ func resolveEnemyAttack(st *combatState, player, enemy *Combatant, phase *Combat
 			Round: st.round, Phase: phaseName, Actor: "consumable", Action: "reflect_damage",
 			Damage: reflected, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
 		})
-		if st.enemyHP <= 0 {
+		if enemyDown(st, phaseName) {
 			return true
 		}
 	}
@@ -1008,6 +1090,108 @@ func applyAbility(st *combatState, player, enemy *Combatant, phase *CombatPhase,
 			Damage: heal, Desc: ab.Name, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
 		})
 
+	case "evade":
+		// The enemy slips out of reach — its next-attacked-against weapon swing
+		// finds nothing. The flag is consumed (and the event emitted) by
+		// resolvePlayerAttack, so a fight log between here and there reads as the
+		// enemy turning evasive and the strike whiffing on the following beat.
+		st.enemyEvadeNext = true
+
+	case "block":
+		// The enemy settles into a parry stance for the rest of the fight: every
+		// player hit from here on rolls a ~50% chance to be halved (on top of any
+		// innate BlockRate). resolvePlayerAttack reads st.enemyBlockUp.
+		if !st.enemyBlockUp {
+			st.enemyBlockUp = true
+			st.events = append(st.events, CombatEvent{
+				Round: st.round, Phase: phaseName, Actor: "enemy", Action: "parry_stance",
+				Desc: ab.Name, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
+			})
+		}
+
+	case "advantage":
+		// The enemy gains the upper hand — it rolls its attacks with advantage
+		// (best of two d20s) for the rest of the fight. resolveEnemyAttack reads
+		// st.enemyAdvantage.
+		if !st.enemyAdvantage {
+			st.enemyAdvantage = true
+			st.events = append(st.events, CombatEvent{
+				Round: st.round, Phase: phaseName, Actor: "enemy", Action: "advantage",
+				Desc: ab.Name, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
+			})
+		}
+
+	case "retaliate":
+		// A damaging aura: from now on a fraction of every player hit is reflected
+		// straight back. resolvePlayerAttack applies the reflected damage per hit.
+		if st.enemyRetaliateFrac < 0.5 {
+			st.enemyRetaliateFrac = 0.5
+			st.events = append(st.events, CombatEvent{
+				Round: st.round, Phase: phaseName, Actor: "enemy", Action: "retaliate_aura",
+				Desc: ab.Name, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
+			})
+		}
+
+	case "regenerate":
+		// The enemy starts knitting its wounds every round. The actual healing
+		// ticks in the round_end phase (turn-based) / round start (auto-resolve);
+		// here we just arm it.
+		if st.enemyRegen == 0 {
+			st.enemyRegen = max(1, enemy.Stats.MaxHP/12)
+			st.events = append(st.events, CombatEvent{
+				Round: st.round, Phase: phaseName, Actor: "enemy", Action: "regenerate",
+				Desc: ab.Name, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
+			})
+		}
+
+	case "survive_at_1":
+		// The enemy cheats death once: the next blow that would drop it to 0
+		// leaves it at 1 HP instead (see enemyDown). Arm it the first time the
+		// ability procs; it stays armed until spent.
+		if !st.enemySurviveArmed {
+			st.enemySurviveArmed = true
+			st.events = append(st.events, CombatEvent{
+				Round: st.round, Phase: phaseName, Actor: "enemy", Action: "survive_armed",
+				Desc: ab.Name, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
+			})
+		}
+
+	case "stat_drain":
+		// Saps the player's strength — a flat, accumulating reduction to the
+		// damage their hits deal. Capped so a long fight can't zero them out.
+		drain := 2 + st.roll(3)
+		st.playerAtkDrain = min(12, st.playerAtkDrain+drain)
+		st.events = append(st.events, CombatEvent{
+			Round: st.round, Phase: phaseName, Actor: "enemy", Action: "stat_drain",
+			Damage: drain, Desc: ab.Name, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
+		})
+
+	case "debuff":
+		// Fouls the player's defence — a flat, accumulating reduction to their
+		// effective AC, so the enemy's attacks land more often. Capped.
+		drain := 1 + st.roll(2)
+		st.playerACDebuff = min(6, st.playerACDebuff+drain)
+		st.events = append(st.events, CombatEvent{
+			Round: st.round, Phase: phaseName, Actor: "enemy", Action: "debuff",
+			Damage: drain, Desc: ab.Name, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
+		})
+
+	case "max_hp_drain":
+		// Drains life force: lowers the player's effective MaxHP and deals that
+		// much immediate damage (the drain hits current HP too). Effective MaxHP
+		// is floored at 1 via the accumulating cap.
+		headroom := max(0, player.Stats.MaxHP-1-st.maxHPDrain)
+		drain := min(headroom, player.Stats.MaxHP/10+st.roll(max(1, player.Stats.MaxHP/20)))
+		st.maxHPDrain += drain
+		st.playerHP = max(0, st.playerHP-drain)
+		st.events = append(st.events, CombatEvent{
+			Round: st.round, Phase: phaseName, Actor: "enemy", Action: "max_hp_drain",
+			Damage: drain, Desc: ab.Name, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
+		})
+		if st.playerHP <= 0 {
+			return !trySave(st, player, phaseName)
+		}
+
 	case "spell_resist", "reveal_action", "fear_immune", "ally_buff":
 		// Slice-2 placeholder: no mechanical effect yet (these need persistent
 		// per-fight state, deferred to the next slice), but the ability still
@@ -1067,6 +1251,36 @@ func playerDefense(player *Combatant, st *combatState) int {
 	return def
 }
 
+// effPlayerMaxHP is the player's MaxHP after any max_hp_drain monster ability,
+// floored at 1. Heal clamps use this so a drained player can't be topped back
+// up past the lowered ceiling. With no drain (every characterization scenario)
+// it returns player.Stats.MaxHP unchanged.
+func effPlayerMaxHP(player *Combatant, st *combatState) int {
+	return max(1, player.Stats.MaxHP-st.maxHPDrain)
+}
+
+// enemyDown reports whether the enemy is actually dead. It is the single choke
+// point every "did this drop the enemy" check routes through, so the
+// survive_at_1 ability can cheat death exactly once: an armed enemy at/below 0
+// HP is restored to 1, the flag is spent, and the fight continues. With no
+// ability armed (every auto-resolve characterization scenario), this is a plain
+// st.enemyHP <= 0 with no side effects.
+func enemyDown(st *combatState, phaseName string) bool {
+	if st.enemyHP > 0 {
+		return false
+	}
+	if st.enemySurviveArmed {
+		st.enemySurviveArmed = false
+		st.enemyHP = 1
+		st.events = append(st.events, CombatEvent{
+			Round: st.round, Phase: phaseName, Actor: "enemy", Action: "survive_at_1",
+			PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
+		})
+		return false
+	}
+	return true
+}
+
 func trySave(st *combatState, player *Combatant, phaseName string) bool {
 	if player.Mods.DeathSave && !st.deathSaveUsed {
 		st.deathSaveUsed = true

internal/plugin/combat_narrative.go

@@ -306,6 +306,32 @@ func renderEvent(e CombatEvent, playerName, enemyName string, result CombatResul
 	case "ability_flavor":
 		return pickRand(narrativeAbilityFlavor)
 
+	// Monster abilities — slice 3 stateful effects
+	case "evade":
+		return pickRand(narrativeEvade)
+	case "parry_stance":
+		return pickRand(narrativeParryStance)
+	case "advantage":
+		return pickRand(narrativeAdvantage)
+	case "retaliate_aura":
+		return pickRand(narrativeRetaliateAura)
+	case "retaliate":
+		return fmt.Sprintf(pickRand(narrativeRetaliate), e.Damage)
+	case "regenerate":
+		return pickRand(narrativeRegenerate)
+	case "regen_tick":
+		return fmt.Sprintf(pickRand(narrativeRegenTick), e.Damage)
+	case "survive_armed":
+		return pickRand(narrativeSurviveArmed)
+	case "survive_at_1":
+		return pickRand(narrativeSurvive)
+	case "stat_drain":
+		return pickRand(narrativeStatDrain)
+	case "debuff":
+		return pickRand(narrativeDebuff)
+	case "max_hp_drain":
+		return fmt.Sprintf(pickRand(narrativeMaxHPDrain), e.Damage)
+
 	case "timeout":
 		return pickRand(narrativeTimeout)
 
@@ -645,6 +671,78 @@ var narrativeAbilityFlavor = []string{
 	"🌀 The enemy invokes a power you can't quite read. File it under 'concerning'.",
 }
 
+var narrativeEvade = []string{
+	"💨 Your strike lands on nothing — the enemy was never quite where it looked.",
+	"💨 The enemy slips the blow. Your weapon finds only the air it left behind.",
+	"💨 A clean swing, a clean miss. The enemy ghosts aside at the last instant.",
+}
+
+var narrativeParryStance = []string{
+	"🛡️ The enemy settles into a tight defensive guard. Hits are going to come harder now.",
+	"🛡️ The enemy raises its guard and *means* it — every blow from here will have to earn it.",
+	"🛡️ The enemy shifts its stance, weapon angled to turn your strikes aside.",
+}
+
+var narrativeAdvantage = []string{
+	"🎯 The enemy reads your rhythm. Its strikes start coming with unsettling certainty.",
+	"🎯 Something clicks for the enemy — it's anticipating you now, and it shows.",
+	"🎯 The enemy presses an advantage you can't quite see. Its aim has sharpened.",
+}
+
+var narrativeRetaliateAura = []string{
+	"🔥 The enemy flares with a punishing aura. Hitting it is about to cost you.",
+	"🔥 A searing field wraps the enemy — every blow you land will bite back.",
+	"🔥 The enemy wreathes itself in retaliation. Strike it and you share the pain.",
+}
+
+var narrativeRetaliate = []string{
+	"🔥 The enemy's aura lashes back — %d damage for the privilege of hitting it.",
+	"🔥 Your strike lands, and the recoil burns. %d damage bounces straight back into you.",
+	"🔥 %d damage reflected. The enemy made you pay for that hit in real time.",
+}
+
+var narrativeRegenerate = []string{
+	"♻️ The enemy's wounds begin to close on their own. This just got slower.",
+	"♻️ Torn flesh knits and seals. The enemy has started regenerating.",
+	"♻️ The enemy's body refuses to stay damaged — it's healing between blows now.",
+}
+
+var narrativeRegenTick = []string{
+	"♻️ The enemy mends another %d HP. The damage you're doing keeps un-doing itself.",
+	"♻️ +%d HP for the enemy as its wounds seal over. Frustrating.",
+	"♻️ The enemy claws back %d HP. You'll have to out-pace the regeneration.",
+}
+
+var narrativeSurviveArmed = []string{
+	"🕯️ The enemy refuses the idea of dying. Something keeps it on its feet past where it should fall.",
+	"🕯️ A grim resilience settles over the enemy — it will not go down easy.",
+	"🕯️ The enemy digs in. Whatever's holding it together, it isn't ready to let go.",
+}
+
+var narrativeSurvive = []string{
+	"🕯️ The killing blow lands clean — and the enemy *stays standing* at 1 HP. Unbelievable.",
+	"🕯️ That should have ended it. The enemy clings to a single point of HP through sheer spite.",
+	"🕯️ The enemy by all rights should be down. It is, instead, very barely up.",
+}
+
+var narrativeStatDrain = []string{
+	"🩸 The enemy saps your strength — your swings feel heavier, weaker. (-%d hit damage)",
+	"🩸 Something drains out of your limbs. Your hits won't bite as deep now. (-%d damage)",
+	"🩸 The enemy leeches your vigour. -%d damage on every strike from here.",
+}
+
+var narrativeDebuff = []string{
+	"😖 The enemy fouls your footing — your guard slips. (-%d AC)",
+	"😖 A wave of something sickly rolls over you. Harder to defend now. (-%d AC)",
+	"😖 The enemy's effect frays your defence. -%d AC, and their hits will notice.",
+}
+
+var narrativeMaxHPDrain = []string{
+	"☠️ The enemy drains your life force — %d HP gone, and your maximum drops with it.",
+	"☠️ Something cold pulls %d HP out of you and won't give it back. Your ceiling just fell.",
+	"☠️ %d HP siphoned away, max and all. There's less of you to work with now.",
+}
+
 // Outcome flavor
 var narrativeNearDeathWin = []string{
 	"You survived by the skin of your teeth. Barely standing. The healers are on standby.",

internal/plugin/combat_session.go

@@ -96,6 +96,20 @@ type CombatStatuses struct {
 	AssassinateReroll bool `json:"assassinate_reroll_used,omitempty"`
 	AssassinateBonus  bool `json:"assassinate_bonus_used,omitempty"`
 
+	// Slice-3 stateful monster-ability effects — armed by applyAbility, read by
+	// the shared resolution primitives, round-tripped through combatState so a
+	// suspended/resumed fight (or a reaper auto-play) keeps the same effect
+	// state. EnemyEvadeNext is a one-shot; the rest persist for the fight.
+	EnemyEvadeNext     bool    `json:"enemy_evade_next,omitempty"`
+	EnemyBlockUp       bool    `json:"enemy_block_up,omitempty"`
+	EnemyAdvantage     bool    `json:"enemy_advantage,omitempty"`
+	EnemyRetaliateFrac float64 `json:"enemy_retaliate_frac,omitempty"`
+	EnemyRegen         int     `json:"enemy_regen,omitempty"`
+	EnemySurviveArmed  bool    `json:"enemy_survive_armed,omitempty"`
+	PlayerAtkDrain     int     `json:"player_atk_drain,omitempty"`
+	PlayerACDebuff     int     `json:"player_ac_debuff,omitempty"`
+	MaxHPDrain         int     `json:"max_hp_drain,omitempty"`
+
 	// Persistent stat buffs from mid-fight !cast / !consume, accumulated as
 	// deltas against the freshly-rebuilt combatant. applySessionBuffs folds
 	// these back onto the player every round; diffTurnBuff produces them.

internal/plugin/combat_turn_engine.go

@@ -133,7 +133,18 @@ func resumeTurnEngine(sess *CombatSession, player, enemy *Combatant, rng *rand.R
 		firstAttackBonusUsed:  sess.Statuses.FirstAtkBonusUsed,
 		assassinateRerollUsed: sess.Statuses.AssassinateReroll,
 		assassinateBonusUsed:  sess.Statuses.AssassinateBonus,
-		rng:                   rng,
+		// Slice-3 stateful monster-ability effects — armed by applyAbility,
+		// round-tripped here so they survive a suspend/resume or reaper auto-play.
+		enemyEvadeNext:     sess.Statuses.EnemyEvadeNext,
+		enemyBlockUp:       sess.Statuses.EnemyBlockUp,
+		enemyAdvantage:     sess.Statuses.EnemyAdvantage,
+		enemyRetaliateFrac: sess.Statuses.EnemyRetaliateFrac,
+		enemyRegen:         sess.Statuses.EnemyRegen,
+		enemySurviveArmed:  sess.Statuses.EnemySurviveArmed,
+		playerAtkDrain:     sess.Statuses.PlayerAtkDrain,
+		playerACDebuff:     sess.Statuses.PlayerACDebuff,
+		maxHPDrain:         sess.Statuses.MaxHPDrain,
+		rng:                rng,
 	}
 	return &turnEngine{
 		sess:   sess,
@@ -181,10 +192,15 @@ func (te *turnEngine) stepPlayerTurn(action PlayerAction) {
 		te.stepPlayerActionEffect(action.Effect)
 		return
 	}
-	// Default: weapon attack. resolvePlayerAttack returns true once the
+	// Default: weapon attack. resolvePlayerAttack returns true once the fight
-	// enemy is down.
+	// is decided — usually the enemy is down, but a retaliate aura can drop the
+	// player on their own swing, so disambiguate the outcome by HP.
 	if resolvePlayerAttack(te.st, te.player, te.enemy, &turnCombatPhase, te.result) {
-		te.finish(CombatStatusWon)
+		if te.st.playerHP <= 0 {
+			te.finish(CombatStatusLost)
+		} else {
+			te.finish(CombatStatusWon)
+		}
 		return
 	}
 	if te.petStrike() {
@@ -213,7 +229,7 @@ func (te *turnEngine) petStrike() bool {
 		Round: st.round, Phase: turnCombatPhase.Name, Actor: "pet", Action: "pet_attack",
 		Damage: petDmg, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
 	})
-	return st.enemyHP <= 0
+	return enemyDown(st, turnCombatPhase.Name)
 }
 
 // rollCombatSessionPetProc makes the one-and-only per-fight pet-attack roll and
@@ -258,7 +274,10 @@ func (te *turnEngine) stepPlayerActionEffect(eff *turnActionEffect) {
 		st.enemyHP = max(0, st.enemyHP-eff.EnemyDamage)
 	}
 	if eff.PlayerHeal > 0 {
-		st.playerHP = min(te.sess.PlayerHPMax, st.playerHP+eff.PlayerHeal)
+		// Respect any max_hp_drain monster ability — a drained player can't be
+		// healed back past the lowered ceiling.
+		hpCap := max(1, te.sess.PlayerHPMax-st.maxHPDrain)
+		st.playerHP = min(hpCap, st.playerHP+eff.PlayerHeal)
 	}
 	action := eff.Action
 	if action == "" {
@@ -268,7 +287,7 @@ func (te *turnEngine) stepPlayerActionEffect(eff *turnActionEffect) {
 		Round: st.round, Phase: turnCombatPhase.Name, Actor: "player", Action: action,
 		Damage: eff.EnemyDamage, PlayerHP: st.playerHP, EnemyHP: st.enemyHP, Desc: eff.Label,
 	})
-	if st.enemyHP <= 0 {
+	if enemyDown(st, turnCombatPhase.Name) {
 		te.finish(CombatStatusWon)
 		return
 	}
@@ -377,6 +396,14 @@ func (te *turnEngine) stepRoundEnd() {
 			}
 		}
 	}
+	// Regenerate (monster ability): the enemy knits its wounds at round end.
+	if st.enemyRegen > 0 && st.enemyHP > 0 && st.enemyHP < te.enemy.Stats.MaxHP {
+		st.enemyHP = min(te.enemy.Stats.MaxHP, st.enemyHP+st.enemyRegen)
+		st.events = append(st.events, CombatEvent{
+			Round: st.round, Phase: CombatPhaseRoundEnd, Actor: "enemy", Action: "regen_tick",
+			Damage: st.enemyRegen, PlayerHP: st.playerHP, EnemyHP: st.enemyHP,
+		})
+	}
 	st.round++
 	te.sess.Phase = CombatPhasePlayerTurn
 }
@@ -422,6 +449,15 @@ func (te *turnEngine) commit() {
 	s.FirstAtkBonusUsed = st.firstAttackBonusUsed
 	s.AssassinateReroll = st.assassinateRerollUsed
 	s.AssassinateBonus = st.assassinateBonusUsed
+	s.EnemyEvadeNext = st.enemyEvadeNext
+	s.EnemyBlockUp = st.enemyBlockUp
+	s.EnemyAdvantage = st.enemyAdvantage
+	s.EnemyRetaliateFrac = st.enemyRetaliateFrac
+	s.EnemyRegen = st.enemyRegen
+	s.EnemySurviveArmed = st.enemySurviveArmed
+	s.PlayerAtkDrain = st.playerAtkDrain
+	s.PlayerACDebuff = st.playerACDebuff
+	s.MaxHPDrain = st.maxHPDrain
 	te.sess.TurnLog = append(te.sess.TurnLog, st.events...)
 }