diff --git a/src/game/skills/impl/ass/skill-266-blade-fury.ts b/src/game/skills/impl/ass/skill-266-blade-fury.ts
new file mode 100644
index 0000000..61380a4
--- /dev/null
+++ b/src/game/skills/impl/ass/skill-266-blade-fury.ts
@@ -0,0 +1,44 @@
+/**
+ * Diablo II: Lord of Destruction v1.13c — Skill #266: Blade Fury (ASS)
+ *
+ * Authoritative 1.13c Ground Truth (`Patch_D2.mpq` -> `data\\global\\excel\\Skills.txt`):
+ * - Skill ID: 266 ("Blade Fury")
+ * - Class: "ass"
+ * - Required Level: 18
+ * - Server Functions: srvstfunc=26, srvdofunc=48, srvprgfunc1=0, srvprgfunc2=0, srvprgfunc3=0
+ * - Associated Missile / State / Summon: missile="bladefragment1", state="", summon=""
+ * - 1.13c Synergy Formulas: EDmgSymPerCalc="", DmgSymPerCalc="", ELenSymPerCalc=""
+ */
+import type {
+  SkillEvalContext,
+  SkillEvalResult,
+  SkillExecContext,
+  SkillExecOutcome,
+  SkillModule,
+} from '../../types.ts'
+import { evaluateSkillCore113c, executeSkillCore113c } from '../../registry.ts'
+
+export const skillModule: SkillModule = {
+  skillId: 266,
+  name: "Blade Fury",
+  charClass: "ass",
+  srvStFunc: 26,
+  srvDoFunc: 48,
+
+  evaluate(ctx: SkillEvalContext): SkillEvalResult {
+    return evaluateSkillCore113c(ctx)
+  },
+
+  executeDo(ctx: SkillExecContext): SkillExecOutcome {
+    const outcome = executeSkillCore113c(ctx)
+    return {
+      ...outcome,
+      notes: [
+        ...outcome.notes,
+        'skill_module:skill-266-blade-fury',
+      ],
+    }
+  },
+}
+
+export default skillModule
diff --git a/tests/skills/ass/skill-266-blade-fury.test.ts b/tests/skills/ass/skill-266-blade-fury.test.ts
new file mode 100644
index 0000000..529c2d5
--- /dev/null
+++ b/tests/skills/ass/skill-266-blade-fury.test.ts
@@ -0,0 +1,109 @@
+/**
+ * 1.13c Numerical & Runtime Verification Suite — Skill #266: Blade Fury (ASS)
+ * Gitea Tracking Issue: #359
+ */
+import { describe, expect, it } from 'vitest'
+import { getSharedDataRegistry } from '../../../src/game/engine/data-registry.ts'
+import { UnitStatList } from '../../../src/game/engine/stat-list.ts'
+import { WorldArena } from '../../../src/game/engine/world-arena.ts'
+import { skillModule } from '../../../src/game/skills/impl/ass/skill-266-blade-fury.ts'
+
+describe('[Skill #266] Blade Fury (ASS) — 1.13c Parity (Issue #359)', () => {
+  it('evaluates exact 1.13c Skills.txt / Missiles.txt formulas at slvl 1, 10, and 20', async () => {
+    const registry = await getSharedDataRegistry()
+    const skillRec = registry.getSkillById(266)!
+    expect(skillRec).toBeDefined()
+    expect(skillModule.skillId).toBe(266)
+    expect(skillModule.name).toBe("Blade Fury")
+    expect(skillModule.charClass).toBe("ass")
+
+    const stats1 = new UnitStatList()
+    stats1.setBaseSkillLevel(266, 1)
+    const r1 = skillModule.evaluate!({ registry, skill: skillRec, slvl: 1, blvl: 1, statList: stats1 })
+    expect(r1.manaCost).toBe(1)
+    expect(r1.manaCost256).toBe(256)
+    expect(r1.minPhysDmg).toBe(8)
+    expect(r1.maxPhysDmg).toBe(10)
+    expect(r1.minElemDmg256).toBe(0)
+    expect(r1.maxElemDmg256).toBe(0)
+
+    const stats10 = new UnitStatList()
+    stats10.setBaseSkillLevel(266, 10)
+    const r10 = skillModule.evaluate!({ registry, skill: skillRec, slvl: 10, blvl: 10, statList: stats10 })
+    expect(r10.manaCost).toBe(2)
+    expect(r10.manaCost256).toBe(544)
+    expect(r10.minPhysDmg).toBe(39)
+    expect(r10.maxPhysDmg).toBe(41)
+    expect(r10.minElemDmg256).toBe(0)
+    expect(r10.maxElemDmg256).toBe(0)
+
+    const stats20 = new UnitStatList()
+    stats20.setBaseSkillLevel(266, 20)
+    const r20 = skillModule.evaluate!({ registry, skill: skillRec, slvl: 20, blvl: 20, statList: stats20 })
+    expect(r20.manaCost).toBe(3)
+    expect(r20.manaCost256).toBe(864)
+    expect(r20.minPhysDmg).toBe(101)
+    expect(r20.maxPhysDmg).toBe(103)
+    expect(r20.minElemDmg256).toBe(0)
+    expect(r20.maxElemDmg256).toBe(0)
+    expect(r20.durationFrames).toBe(0)
+    expect(r20.radiusSubtiles).toBe(0)
+    expect(r20.petMax).toBe(0)
+    expect(r20.cooldownFrames).toBe(0)
+  })
+
+  it('enforces 1.13c blvl synergy rule (hard points boost synergy; +skills and item charges do NOT)', async () => {
+    const registry = await getSharedDataRegistry()
+    const skillRec = registry.getSkillById(266)!
+    const synId = null
+
+    const statsBase = new UnitStatList()
+    statsBase.setBaseSkillLevel(266, 20)
+    if (synId !== null) {
+      statsBase.setBaseSkillLevel(synId, 20)
+    }
+    const withHardPoints = skillModule.evaluate!({
+      registry,
+      skill: skillRec,
+      slvl: 20,
+      blvl: 20,
+      statList: statsBase,
+    })
+    expect(withHardPoints.synergyBonusPct).toBe(0)
+
+    // +20 allskills and +33 Marrowwalk charges without hard points must yield 0 synergy
+    const statsSoftOnly = new UnitStatList()
+    statsSoftOnly.setBaseSkillLevel(266, 20)
+    statsSoftOnly.addStat('item_allskills', 20)
+    if (synId !== null) {
+      statsSoftOnly.setChargedSkillLevel(synId, 33)
+    }
+    const withSoftOnly = skillModule.evaluate!({
+      registry,
+      skill: skillRec,
+      slvl: 20,
+      blvl: 20,
+      statList: statsSoftOnly,
+    })
+    expect(withSoftOnly.synergyBonusPct).toBe(0)
+  })
+
+  it('executes runtime skill effect in WorldArena (castCount, action frame, and combat/state/missile/summon outcome)', async () => {
+    const registry = await getSharedDataRegistry()
+    const arena = new WorldArena({
+      registry,
+      classCode: "ass",
+      skillId: 266,
+      slvl: 20,
+    })
+    const outcome = arena.triggerCast()
+    arena.stepTicks(15)
+    const dbg = arena.getDebugState()
+
+    expect(dbg.ready).toBe(true)
+    expect(dbg.skillId).toBe(266)
+    expect(dbg.castCount).toBeGreaterThanOrEqual(1)
+    expect(dbg.actionFrameTriggered).toBe(true)
+    expect(outcome?.executed).toBe(true)
+  })
+})