diff --git a/internal/plugin/dnd_subclass_combat.go b/internal/plugin/dnd_subclass_combat.go
index d8e2271..c0c6182 100644
--- a/internal/plugin/dnd_subclass_combat.go
+++ b/internal/plugin/dnd_subclass_combat.go
@@ -17,11 +17,44 @@ func applySubclassPassives(stats *CombatStats, mods *CombatModifiers, c *DnDChar
 	}
 	switch c.Subclass {
 	case SubclassChampion:
-		// L5 Improved Critical: crit on nat 19+. SUB3 Superior Critical
-		// (L15) will lower this to 18.
+		// L5 Improved Critical: crit on nat 19+. L15 Superior Critical
+		// lowers this further to 18.
 		if c.Level >= 5 {
 			mods.CritThreshold = 19
 		}
+		// Phase 10 SUB3a-i — L10 Additional Fighting Style. 5e lets the
+		// player pick a second style; in 1v1 we can't surface a UI for
+		// that, so we collapse to the two most generally useful
+		// approximations stacked: Defense (+1 AC) and Dueling (+10%
+		// damage when one-handed — we don't track grip state, so this is
+		// a flat damage bump regardless).
+		if c.Level >= 10 {
+			stats.AC++
+			mods.DamageBonus += 0.10
+		}
+		// Phase 10 SUB3a-i — L15 Superior Critical: crit floor drops to 18.
+		if c.Level >= 15 {
+			mods.CritThreshold = 18
+		}
+	case SubclassBerserker:
+		// L5/L7 Berserker is rage-driven (active ability — see init() below)
+		// plus L7 Mindless Rage which is condition immunity, irrelevant in
+		// our 1v1 model. Phase 10 SUB3a-i adds the always-on L10/L15 layer.
+		//
+		// L10 Intimidating Presence: 5e is an Action that frightens one
+		// target on a failed WIS save. One-shot combat has no action
+		// economy to spend on a non-damage Action, so we proxy as 2 rounds
+		// of 15% enemy miss chance via SporeCloud (the same channel
+		// fog-cloud / Cloak of Shadows uses).
+		// L15 Retaliation: 5e Reaction — when struck in melee, one melee
+		// attack back. We don't model reactions, so the average per-fight
+		// damage uplift is approximated as a +15% damage multiplier.
+		if c.Level >= 10 {
+			mods.SporeCloud += 2
+		}
+		if c.Level >= 15 {
+			mods.DamageBonus += 0.15
+		}
 	case SubclassBattleMaster:
 		// L7 Know Your Enemy: 5e gives factual info about the target after
 		// 1 min observation. We don't model "observation time" — proxy the
diff --git a/internal/plugin/dnd_subclass_combat_test.go b/internal/plugin/dnd_subclass_combat_test.go
index 4e6d144..4554c65 100644
--- a/internal/plugin/dnd_subclass_combat_test.go
+++ b/internal/plugin/dnd_subclass_combat_test.go
@@ -868,3 +868,76 @@ func TestCharacterActiveAbilities_RageVisibility(t *testing.T) {
 	}
 }
 
+// ── SUB3a-i — Champion + Berserker L10/L15 ──────────────────────────────
+
+func TestApplySubclassPassives_ChampionL10AdditionalFightingStyle(t *testing.T) {
+	c := &DnDCharacter{Class: ClassFighter, Subclass: SubclassChampion, Level: 10}
+	stats := &CombatStats{AC: 16}
+	mods := &CombatModifiers{DamageReduct: 1.0}
+	applySubclassPassives(stats, mods, c)
+	if stats.AC != 17 {
+		t.Errorf("L10 Champion AC = %d, want 17 (+1 Defense style)", stats.AC)
+	}
+	if mods.DamageBonus < 0.099 || mods.DamageBonus > 0.101 {
+		t.Errorf("L10 Champion DamageBonus = %v, want ~0.10 (Dueling style)", mods.DamageBonus)
+	}
+	// L5 Improved Critical still in effect; L15 hasn't yet kicked in.
+	if mods.CritThreshold != 19 {
+		t.Errorf("L10 Champion CritThreshold = %d, want 19 (L15 not yet)", mods.CritThreshold)
+	}
+}
+
+func TestApplySubclassPassives_ChampionL9NoFightingStyle(t *testing.T) {
+	c := &DnDCharacter{Class: ClassFighter, Subclass: SubclassChampion, Level: 9}
+	stats := &CombatStats{AC: 16}
+	mods := &CombatModifiers{DamageReduct: 1.0}
+	applySubclassPassives(stats, mods, c)
+	if stats.AC != 16 {
+		t.Errorf("L9 Champion AC = %d, want 16 (Fighting Style gates at L10)", stats.AC)
+	}
+	if mods.DamageBonus != 0 {
+		t.Errorf("L9 Champion DamageBonus = %v, want 0", mods.DamageBonus)
+	}
+}
+
+func TestApplySubclassPassives_ChampionL15SuperiorCritical(t *testing.T) {
+	c := &DnDCharacter{Class: ClassFighter, Subclass: SubclassChampion, Level: 15}
+	mods := &CombatModifiers{DamageReduct: 1.0}
+	applySubclassPassives(&CombatStats{AC: 16}, mods, c)
+	if mods.CritThreshold != 18 {
+		t.Errorf("L15 Champion CritThreshold = %d, want 18 (Superior Critical)", mods.CritThreshold)
+	}
+}
+
+func TestApplySubclassPassives_BerserkerL10IntimidatingPresence(t *testing.T) {
+	c := &DnDCharacter{Class: ClassFighter, Subclass: SubclassBerserker, Level: 10}
+	mods := &CombatModifiers{DamageReduct: 1.0}
+	applySubclassPassives(&CombatStats{}, mods, c)
+	if mods.SporeCloud != 2 {
+		t.Errorf("L10 Berserker SporeCloud = %d, want 2 (Intimidating Presence)", mods.SporeCloud)
+	}
+	if mods.DamageBonus != 0 {
+		t.Errorf("L10 Berserker DamageBonus = %v, want 0 (Retaliation gates at L15)", mods.DamageBonus)
+	}
+}
+
+func TestApplySubclassPassives_BerserkerL9NoIntimidatingPresence(t *testing.T) {
+	c := &DnDCharacter{Class: ClassFighter, Subclass: SubclassBerserker, Level: 9}
+	mods := &CombatModifiers{DamageReduct: 1.0}
+	applySubclassPassives(&CombatStats{}, mods, c)
+	if mods.SporeCloud != 0 {
+		t.Errorf("L9 Berserker SporeCloud = %d, want 0", mods.SporeCloud)
+	}
+}
+
+func TestApplySubclassPassives_BerserkerL15Retaliation(t *testing.T) {
+	c := &DnDCharacter{Class: ClassFighter, Subclass: SubclassBerserker, Level: 15}
+	mods := &CombatModifiers{DamageReduct: 1.0}
+	applySubclassPassives(&CombatStats{}, mods, c)
+	if mods.DamageBonus < 0.149 || mods.DamageBonus > 0.151 {
+		t.Errorf("L15 Berserker DamageBonus = %v, want ~0.15 (Retaliation)", mods.DamageBonus)
+	}
+	if mods.SporeCloud != 2 {
+		t.Errorf("L15 Berserker SporeCloud = %d, want 2 (L10 still active)", mods.SporeCloud)
+	}
+}